It's going to be a simulcast of Talk 1200. I'll bet on it. They're investing money in that station, and aren't going to let it sit there only on 1200, especially with its lack of night signal in the city.
101.7 gives it an FM presence and most importantly, building penetration in the city itself. Sure 101.7 is a class A directional signal, but it puts a 70+dBu signal into all of Boston. That gets them inside any 99% of buildings, plus portable radios and "walkman" style or whatever they're called now. Things with earbuds. 1200 reaches the western suburbs okay, it's the signal inside the city that they want. Conservative talk may have listeners that live in the burbs, but a lot of them work and/or do things in the city itself. You can't hear 1200 in the tunnels, which is a lot of the city now! 101.7 is on the tunnel repeater system. If you commute in or through Boston, you spend a lot of time in a tunnel.
On the financial side, it doesn't cost them any more to run 1200/101.7 than 1200 alone, except the tower rent and electric bill (which is small at their TPO) and the benefits will be more listeners and higher ad rates. The only hires might be extra sales people to sell more spots. Everything else is in place, from air staff to promotions and any other support staff.
Urban AC would cost money to operate, as an airstaff, promotions staff and sales staff would have to be put in place. Mia 1430 won't generate the cash and publicity that "Talk 101.7/1200" would, because if you're not Spanish speaking, you don't care.