Zero chance of any LPFM's in Boston or anywhere out to 128 and, in most cases, out to 495. The dial is just far too packed.
Almost certainly zero chance in any Top 20 market. Very low chance of any new LPFM's in markets down to around #50 or #60...depends somewhat on the market. Oddly enough, even in pretty rural areas, sometimes you're squeezed between two other, medium markets and you can find yourself with no possibilities for LPFM's because of all the rimshotters. And of course, anywhere near a real population center, you're going to find numerous applicants all fighting over just ONE (maybe two) license. And odds are good a time-sharing situation will occur and that generally makes for terrible radio listening; if the owners could've gotten along and collaborated in the first place, there wouldn't have been a time-share.
LPFM was always a bad idea to a real problem. The real answer would have been re-instituting some actual ownership caps instead of the joke that TelComm'96 made them. Instead there was a collective hallucination that if you made a signal small and economically crippled enough, then it would be cheap enough for low-budget "community broadcasters" to somehow scrape together just enough money to get started despite having no real business plan. Quite a few LPFM's have folded an returned their licenses to the FCC since 2000 because they either had a weak business plan or, equally likely, the community they were in just wasn't going to support another radio station.
At this point, the justification for LPFM is very, very low. Most radio listening is done in the car, which an LPFM is poorly-suited for since the signal...by definition...is not meant to cover more than 5.6km radius. The only places where you still see a lot of non-car radio listening is in urban areas with high population density, congested roads, and passable-to-decent public transit. Places where it will, for the most part, be impossible to fit an LPFM. Put that together and add in that there's rarely going to be high demand for a new radio station when any underserved audience is probably getting what they want from satellite radio or internet radio? Very hard to justify a new, small radio station like an LPFM.
As for Boston, I should point out that for most of 1998 to 2005, a lot of the college radio stations in eastern Mass had very weak management structures and they welcomed community volunteers to help out...especially over the summers. A dozen or so organized and shrewd community volunteers could easily have come in, set up shop, and gradually (2 or 3 years) taken over all the aspects that mattered at the station, while still preserving enough student involvement to keep the parent college happy. Granted, that would not work at WHRB, WMBR or WZBC, but those are about 20 times bigger signals than any LPFM's anyways. Since 2005, it's gotten tougher as several colleges have invested more time and money into their stations, and would be sensitive to a takeover attempt (no matter how subtle) by an "outside entity".
That said, there's still likely a lot of potential for community volunteers to just come in and do a decent show at stations like WMFO, WBRS, and even WZBC. You might need to come in at a really ungodly hour but sometimes that "ungodly hour" is prime drivetime around 5 to 7am.