The Boston area currently has 2 Service Centers. From all I've heard from local owners, at least one of those SC's is cramped and regularly full.
But they've also stated that they've heard the search is on for a new location.
And just using some anecdotal evidence (my eyes), some of the immediate north and west suburbs of Boston (Weston, Lincoln, Sudbury, Carlisle, Concord, etc) already have a decent concentration of Teslas. Add in the Model 3, and the need for a larger Service Center in that area becomes apparent. I don't know if we'll end up with 3 Service Centers..all signs point to Tesla closing the Watertown SC and moving somewhere with a larger footprint.
(Selfishly, I wouldn't mind them being on the NW side of 128/95, as that would put me within 20 minutes of one).