To sense true yearning for a united Ireland in Dublin you used to have to run your fingers over words written long ago and etched in cold, grey stone. “No man has a right to fix the boundary to the march of a nation. No man has a right to say to his country: ‘Thus far shalt thou go and no further’.”

So declared Charles Stewart Parnell in 1885 in an exhortation engraved in his granite monument on O’Connell Street. Quotes pining for nationhood from other nationalist leaders adorn similar monuments around the city.

Most predate Ireland’s partition in 1922 but they resonated as aspirations to unite the 26-county south with the six counties of Northern Ireland – aspirations which southerners, as decades passed, espoused with dwindling conviction. There were other priorities: emigration, jobs, the economy, the health service. And in any case a united Ireland was never going to happen.

Until it was.

These days you open a newspaper, turn on the television, perch on a bar stool and the topic bubbles up not as history but as a looming existential choice, the forsaken dream dusted off and glimmering as possible – even inevitable.

“It’s like a ball or boulder coming down the hill. You can’t stop it,” said Osgur Breatnach, an author and political activist at a book-reading in south county Dublin. “Agree with it or not, it’s going to happen.”

Drinkers in the Pádraig Pearse, an inner city pub and republican haunt named after one of the leaders of the 1916 Easter rising, cheered the prospect. “A united republic of Ireland – I’d love it,” said Jamie Dean, 60, a labourer. “We’d be the same country. Not the Brits. It’s ours. So simple.”

It’s not simple.

Northern Ireland Unionists and Protestants who consider themselves British recoil at the idea of a United Ireland. Plenty of Catholics north and south have their own reservations, not least the financial cost, adding up to a fraught, complex tangle of identity, ideology and economics.

But a confluence of events has shunted unification on to the political agenda.

Despite its citizens having voted 56% to stay in the European Union, Northern Ireland’s economy and constitutional scaffolding is now being buffeted by Brexit winds, scaffolding that was already wobbling because of a breakdown in the Stormont power-sharing government which has left a vacuum for more than 600 days.

A plan unveiled last week by the European Research Group – the hard Brexit faction of the Conservative party – failed to assuage anxiety over whether a hard or soft border will descend on the porous 310-mile boundary of fields, roads and towns.

Being bounced out of the EU to an uncertain fate has prompted one in six Northern Ireland voters to switch allegiance, delivering a majority for unification, according to a recent poll. “The possibility is no longer a pipe dream,” said Tommy McKearney, 66, a former IRA member and hunger striker. “I don’t think it’s imminent. It’ll be over the next 20 to 30 years – in a lifetime, but not in my lifetime.”

Demography is key. When British negotiators carved Northern Ireland from the newly independent south it was 65% Protestant, 35% Catholic, entrenching a unionist majority. A century later it is 48% Protestant, 45% Catholic. Unionists remain the biggest bloc, but are not an overall electoral majority. In last year’s general election the Democratic Unionist Party won a mere 1,168 more votes than Sinn Fein.

“It’s a massive demographic shift. In five to 10 years there’ll be a Catholic majority in Northern Ireland,” said Peter Shirlow, director of the University of Liverpool’s Institute of Irish Studies. It will take longer for those numbers to translate into the electorate. “But a majority for a united Ireland is going to happen, no doubt about that.”

Some unionists are overturning taboos by openly questioning the endurance and even desirability of the union with Britain.

The “battle for the union is on”, Peter Robinson, Northern Ireland’s former first minister, and former leader of the Democratic Unionist Party, recently warned. Unionists need to prepare for a border poll, he said: “I don’t expect my own house to burn down, but I still insure it because it could happen.” Unionists, in other words, need to act before the demographic clock ticks to midnight by selling the union’s merits to moderate nationalists and those who consider themselves neither unionist nor nationalist. Brexit, and unionist clumsiness in wooing allies, may immolate such insurance.

A trickle of other prominent unionists such as Alex Kane, Mike Nesbitt and Jim Dornan have joined Robinson in sounding the alarm.

Under the Good Friday agreement, the Northern Ireland secretary should call a border poll if he or she thinks a majority would vote for unification.

The current secretary, Karen Bradley, did not help the union’s case this month by admitting that when appointed to the job she was “slightly scared” of Northern Ireland and profoundly ignorant about its political divisions.

Shoppers on Grafton Street in Dublin. Prosperity has changed the unification equation. Photograph: Bloomberg/Getty

Reaction on the streets of Belfast was scornful. “The government in Westminster doesn’t give a damn about us,” said Tom Neill, 72, a former soldier. “We’re a stepping stone here, politicians drop in, then leave,” said Anthony Quinn, 55, a film location manager.

A spate of anniversaries underscores a sense that eras end, new ones begin, history advances. It is 20 years since the Good Friday agreement cemented republican and loyalist ceasefires with a power-sharing government in Stormont. Next year it is 50 years since the Troubles erupted, three decades of strife which claimed more than 3,500 lives.

Further back, in October it will be 700 years since Edward Bruce, the last high king of Ireland, was defeated at the battle of Faughart and had his head delivered to King Edward II, marking an end to efforts to unite Gaelic Ireland.

When British royals visit Ireland these days they receive hugs. The rebellious colony of uprisings, famine and resentment is now a prosperous, confident republic which no longer defines its identity in opposition to Britishness. Adoring crowds mobbed Prince Harry and Meghan Markle in Dublin in July, a sequel to the Queen’s groundbreaking visit in 2011. Pope Francis, in contrast, spent much of his visit last month apologising for clerical sex abuse.

All changed, changed utterly, as Yeats said.

A country once viewed as an economic basket case and Catholic theocracy is now the EU’s star performer and a secular, progressive beacon with a gay taoiseach, marriage equality and relaxed abortion laws.

In the Pádraig Pearse pub you still find a gate from Kilmainham jail, in honour of the 1916 rebels executed in the prison, but this part of Dublin is transformed, with dank slums giving way to sleek apartments and cafes serving organic avocado toast to Facebook and Google employees.

The republic’s new Garda commissioner is Drew Harris, OBE, a veteran of the Police Service of Northern Ireland and its predecessor, the Royal Ulster Constabulary, which republicans branded a unionist jackboot. The switch in allegiance stirred little controversy.

Nor is there any outcry over Fianna Fail, one of the Republic’s biggest political parties, preparing to become an all-Ireland party by absorbing the SDLP, the north’s moderate nationalist party.

Sinn Fein, the political wing of the IRA during the Troubles, is pushing for a border poll while trying to ease the sting for unionists. A draft document entitled Irish Unity – An Activist’s Guide floats changing the Irish flag and anthem. The party’s leader, Mary Lou McDonald, has suggested rejoining the Commonwealth.

Meanwhile her predecessor, Gerry Adams, a bogeyman for unionists, is cultivating a quirkier persona. His latest initiative: a cookery book with recipes which sustained republicans during marathon peace negotiations. The puns have flowed: “give peas a chance”, “shinner of beef”, “when hunger strikes”.

Unity is coming, said Danny Morrison, a writer and former IRA member and Sinn Fein publicity director. “In socioeconomic terms it makes sense. A majority is emerging that will favour radical change.”

Unionists – if they engaged – could shape the process from a position of strength, he said: “They’re not under duress, they’re not being bombed into it by the IRA.” The new dispensation could be fluid; for instance, an interim phase could keep Stormont and not force unionists to sit in a Dublin parliament.

Unionists with business, farming and fishing interests would be pragmatic if a united Ireland was the only way to remain in the EU, said Morrison. “They’re willing to adapt to that,” he said.

All-Ireland sports act as a bridge, especially when teams do well, such as last month when the women’s hockey team advanced to the World Cup finals, casting a feelgood glow over the whole island.

“It’s now an evidence-based proposition,” said Kevin Meagher, a former Labour adviser on Northern Irelandand author of A United Ireland: Why Unification is Inevitable and How it Will Come About. “There’s a very good utilitarian argument. And it’s now harder to rally against the south as a bogeyman.” British politics will not lament Northern Ireland’s exit from the UK, said Meaghar: “There will be an audible sigh of relief.” It could all add up to a new era – an island re-united belting out Four Green Fields, the folk song about a lost province. But this scenario has a problem.

Whoever voted to be a minority? It’s emotional. It won’t be a reasoned debate Peter Shirlow, Liverpool university

“It’s a load of steaming bollocks. The Orangemen, for starters, won’t be budging.” The speaker is a plasterer called Michael, sipping cider in the Pádraig Pearse.

Many agree with this assessment, albeit with less colourful language. A chorus of politicians, academics, pollsters and even republicans say Brexit’s impact on unionism is overstated and that a united Ireland will not happen soon, if ever.

One reason is the estimated £10bn annual subvention from London to Belfast. Dublin cannot match this. Unification would in all probability mean slashing public sector jobs and services in the north and hiking taxes in the south, incentives for voters on both sides of the border to vote no.

Analysts question the methodology of polls which rely on online panels and show a spike in support for unification. “Most people here take them with a grain of salt,” said Duncan Morrow, an Ulster University professor. Younger unionists may sigh at DUP fulminations against gay marriage and abortion rights, but that doesn’t necessarily mean they wish to join their socially liberal neighbour, he said.

About 40% of Northern Ireland’s electorate does not vote, of which most are unionist, said Shirlow of Liverpool University. A border referendum would galvanise them to vote no, he said. “Whoever voted to be a minority? It’s emotional. It won’t be a reasoned debate, it’s not about evidence or what’s the better society. Our surveys show Brexit hasn’t really changed anybody’s views.”

For all the Republic’s current progressive sheen, unionists are wary of a neighbour which kowtowed to Catholic bishops and marginalised its Protestant minority. “We were kept very quiet and almost disappeared,” said Robin Bury, author of Buried Lives: the Protestants of Southern Ireland. “There is still Anglophobia here, it’s still in the bloodstream. Unionist unease is justified,” he said.

Ian Marshall, an anti-Brexit northern unionist and farmer, has good things to say about the Republic. The Irish government and Sinn Fein supported his election to the Seanad, Dublin’s upper chamber. Yet Marshall warns unification could create a “bloodbath” if loyalists feel alienated or pressured: “We could potentially turn the tap on again, and that fills me with horror.”

Edward Burke, a terrorism expert at Nottingham University, echoed that concern, saying loyalist paramilitaries focused on criminal enterprises could revert to “Pavlovian instincts” of sectarian killing.

“Tiocfaidh ár lá,” goes the republican slogan. Our day will come. An expression of longing masquerading as prophecy. Maybe it will come. But Ireland’s dreamers will need to be patient. And careful what they wish for.