It will for sure not be for connecting passengers, there are basically no connections available with *A. It will be for passengers from/to parts of Manhattan, Brooklyn, Queens, Long Island and Westchester County (+Connecticut).
SAS will cover quite a big area in New Jersey, New York, Connecticut and Massachusetts with EWR, JFK and BOS, so might be a smart move?

It's apparently going to be Terminal 7 so I wonder if there is going to be a lounge available?
BA has lounges there but they are joining AA in terminal 8. That leaves the AS lounge (its a PP lounge by the way) but they might also leave for T8 (I don't know if they are) as terminal 7 is planned to be demolished (Hopefully not while SAS is still there
Quite a lot of interesting questions up in the air.