A Line is the most probable due to being 31 miles long or the 7 line for its tie in to LIRR DLC at Woodside and Mets-Willets Point.
I think the proper time to do and release this would be during the release of the MTA's new R211 train. That way the developers and designers have a full year to build the extension and integrate a brand new train to master.
What Subway lines what ya like to see come on TSW I think the Broadway Lines & Sixth Avenue Lines N,Q,R,W & The B,D,F,M
I think the MTA doesn't want the NYC Subway in the game due to security reasons "Seems like the MTA are worried that if you play this game, you might hijack a subway train!"
I think that’s a poor reason of an excuse to not want Their iconic Subway trains in a game I think it would be amazing