Maybe they can put in a unique railway rifle that fires 4 railwayspikes instead of one in one of the stations.
That is my only complaint about FONV; no Metro... I really enjoyed that in FO3. Most likely it will be in FO4.
Considering that the T is a rather large part of Boston life... yeah, they really need to include something. Quite a bit of it is surface rail irl.
Even if it's handled the way the monorail was in New Vegas, it should really be a part of the game.