There is a hint of the 1970s about the Republic’s new debate on a united Ireland – specifically the years from 1974, when loyalism and unionism came together to wreck experiments in powersharing with a cross-Border dimension, then scratched their heads over what to do next.

All sorts of notions were given serious consideration, from reuniting ancient Ulster to doomsday scenarios of repartition. But the main theme to emerge was an independent Northern Ireland, in forms ranging from dominion status to a unilateral declaration of independence (what today would be called a hard Nirexit.)

For a brief moment in 1975 this pan-unionist movement captured the ballot box and the street. But it could not be sustained, because the unionist population found all these ideas implausible, undesirable or ridiculous.

Now it is the South’s turn for constitutional over-creativity. An independent Northern Ireland has been mentioned, as has joint authority, but the main theme to emerge is of Northern Ireland surviving in some sort of federal or quasi-federal united Ireland.

Gerry Adams has said this could be transitional or a permanent arrangement. Micheál Martin says it would be “a reverse to where we are now”, with London and Dublin swapping roles.

Autonomous region

It is not unusual for a country to have one special autonomous region, although calling it a federation might be rather grand. What makes the idea of Northern Ireland’s continued existence implausible is that, as a region, it would have no purpose.

A federal Ireland is generally proposed as a concession to unionists, but as it can only come about through unionists being outvoted in the North, what autonomy would they have?

No consideration is being given to how Northern nationalists might feel, having finally reached the promised land only to find themselves still stuck in a regional stalemate. Presumably they would just walk away from Stormont, as Sinn Féin has already done. What then?

Neither community has been asked for their view – at least not since the mid-1980s, when Adams ditched Sinn Féin’s policy for a four-province federation because it had no electoral appeal.

If nobody in the North really wants a federal Ireland, its attraction to the South is clearly the preservation of a cordon sanitaire around a lunatic asylum.

Loyalist violence

Concerns have been raised about the threat of loyalist violence, although Southerners should note this is barely an issue for Northern nationalists. Sinn Féin has persuaded its supporters that Britain directed every act of loyalist violence throughout the Troubles, so an end to British rule means no more loyalism – all rather convenient, to put it mildly.

A better reason for optimism is the example of the 1970s, when loyalists considered then abandoned every scenario they could think of for resisting Irish unity by force – and that was when they were at their strongest, with tacit support from the unionist electorate.

All loyalists do now is wreck their own neighbourhoods and shoot each other, while unionism looks the other way. Their likeliest future in a united Ireland mirrors Dublin’s criminal gangs.

Southerners need to accept that if unity happens, the asylum wall comes down. Northern Ireland was created to encompass a British majority inside the UK. This is no more of a “sectarian gerrymander” than any nation drawing a border around itself.

Nevertheless, if the majority evaporates, the Border becomes unsustainable. Nationalists will want it gone and unionists will see no point to it. The Northern Ireland identity is associated with centrist voters, and although they will be the decisive demographic in a Border poll, there are not numerous enough for their identity to prevail.

The likeliest outcome of this will be a unitary state, with a national minority that looks to the neighbouring state – a common scenario across the world. In the proportions applicable to a united Ireland, which would have a 15 per cent British minority, a standard political system emerges: the bulk of the population votes along conventional left-right lines, while the minority elects a purely ethnic party or bloc and hopes to hold the balance of power.

Unless Ireland wants to deal with the DUP forever, one detail that might be considered is a Scottish-style top-up list in elections, which should encourage unionists to vote for multiple parties. Chances are all these parties would still be unionist, however, and at some point they will be in a position to make demands.

Last December, in a snap election, Macedonia’s conservative and social democrat parties won 51 and 49 seats respectively. Neither can form a government without the Albanian ethnic bloc, whose three parties represent a 20 per cent national minority.

The Albanian price for coalition is nationwide recognition of their language - an argument Northern Ireland will find familiar.

The social democrats have agreed, so the conservatives have brought protesters onto the streets, while the ex-conservative president has refused to summon a government, causing a constitutional crisis.

This is the test Irish unity presents: when the Macedonian moment arrives, will the British minority get its way?