In 2015, San Francisco supervisor turned state Sen. Scott Wiener said “San Francisco should always have a subway under construction.”

Actually, Wiener credits that mandate to a friend. But by endorsing the seemingly way-out idea, he put a little extra shine on it. Right now we do indeed have a multi-million dollar, 1.7 mile Central Subway under construction that, once finished, will connect Bayview to Chinatown. But what about when that mega-project finishes? Whither goes the city’s grand designs then?

In the past, the T-Third Street plan stretched as far south as Bayshore and as far north as Fisherman’s Wharf, both underserved neighborhoods despite the presence of Caltrain and Muni streetcar lines.

Should the big dig go further than Chinatown and Bayview next? Or should San Francisco be boring tunnels west toward neighborhoods like the Richmond, hobbled as it is by reliance on chronically packed overland buses?

Maybe the city put that money toward something more attainable, like moving the M Ocean View line underground for part of its sojourn south of West Portal, as SFMTA has pondered in the past?

Or how would commuters like the idea of a 16th Street Muni tunnel connecting the Castro to ever-growing Mission Bay? If you had the power and the funding, where would you make tracks?

Let’s not neglect BART in the equation either. The tantalizing but ever elusive necessity of a San Jose Station becomes more needful by the year.

And who can forget the crazy genius of that imagined 2050 BART map that even included a Marin County line?

More humble suggestions might have merit too. Attorney Josh Arce’s pitch for a 30th and Mission BART station didn’t win him much luck at the ballot box when he ran for Board of Supervisors last year, and almost certainly wouldn’t have happened even if he’d won.

But he wasn’t wrong when he pointed out that the stretch between 24th Street Station and Glen Park is the longest gap in the agency’s SF line, and the city has pondered an in-fill station there for nearly 15 years now.

Putting aside pesky problems like money and politics for a moment, what community in San Francisco—or the larger Bay Area—needs a timely subway extension the most? Let us know in the comments.