Educational Media Foundation, the parent company of K-Love and Air 1, only buys FM stations. Sometimes they are full power, in the commercial band (92-108). Sometimes they are lesser power, rim shot or in the non-commercial band (88-92). But in each case, it's a distress sale.
Last year, EMF bought 106.9 in Hartford, WCCC, with a full Class B signal. But the owner was a stand-alone guy, getting older. (He had owned the station for decades, running it on the cheap, with Howard Stern as his morning host when Howard was beginning his radio career.) The station had gone through several aspects of Rock, Active Rock, Classic Rock, but was doing poorly in the ratings against better run and bigger companies. A similar story centered on 106.9 in Philadelphia. Bad ratings, stand alone operation. I don't think such an FM station exists in Boston.
Yes, there are some rimshot stand-alones mentioned above, 99.1, 104.9, etc. Would Entercom sell off WKAF, figuring the WAAF signal doesn't get that much help from 97.7? It's possible. In NYC, Cox Radio decided to sell off 96.7 which had been a Connecticut based station, after it got FCC permission to move it a bit closer to NYC, making its City of License a community in Westchester. So now some NYC listeners can hear K-Love on that outlet.
But it would have to be that sort of scenario, for K-Love to buy a Boston-area outlet.