Honestly, what's happening in Boston right now reminds me of what was happening with the dial during the early to mid 80's, where you had a revolving door of top-40 stations trying to play 'king of the mountain' all at one time. At one time, I recall, Kiss 108, WHTT, WZOU at and WKKT were all playing the hits at the same time. Kiss was the heritage, as it is now, and prevailed while WHTT had a very short stint at 'Q103' before finding a place as Oldies. WZOU found it's niche as Jam'n when there was absolutely no urban radio in Boston at the time. WKKT found stability as WZLX.
My picks over the next eyar or so...Kiss and Jam'n prevail due to their heritage. Amp indeed goed back to classic/variety hits 'Jack/Mike' type format, 96.9 skews more toward a more grown up/old school/urban AC sound (as much as Boston's demos will permit).
Also, Evolution? I'll give Clear Channel credit for trying to bring the EDM sound to the mainstream on a 24 hour format, though I don't know if it will stick. Bring La Mia up from the AM to 101.7 would be a home run here.
WRKO should look into getting an FM translator with a decent signal covering just the 617/781 area codes.
As much as I am a rock fan, let's admit it, the market was saturated for years. WAAF, WZLX and WBOS are different enough to compliment eachother and with WHJY and WGIR sending decent signals over the metro from their markets, not to mention The River and a bunch of college stations, Boston still has plenty of choices to fill their car settings.
As for easy listening/smooth jazz, etc. Yes, I to am surprised a format hasn't yet evolved to fill that void. I'm sure in this day and age, people really do want to mellow out every now and then. Only time will tell.