As far as a translator within "the belt", if the 103.7 from gloucester keeps moving south, you could see that become a inner-city translator.
Not on 103.7 it can't. It'd run into Intermediate Frequency problems with 92.9 on the Pru (see
74.1204) Plus there's 2nd adjacent concerns with WODS on 103.3...although theoretically it might be possible to base the translator's radiating antenna high enough in the air that the interference zone doesn't reach the ground. More than a few translators have squeaked onto the dial that way. I've said for years that it might...emphasis on "might"...be possible to squeeze a translator onto 89.3 using that method. Put it on top of OFC and co-locate with WERS; the D/U ratio will be plenty favorable enough that it won't cause problems to WERS, and it's high enough that you could...theoretically...use a multi-bay array to keep the interference to WGBH above the ground. Although a big problem would be physical space on the towers (and the transmitter space) on OFC, which is very, very tight. Even a diplex might be tricky because there may not be enough room for the combiners and filters down below.
The problem, of course, with ANY translator...old or new...trying to get into Boston is
47 CFR 74.1203, which basically says that any reports of any interference that can be tied to the new (or recently moved) translator are sufficient to force the translator to move or, if moving is impossible, to shut down. The dial in Boston is so packed that it's impossible for any new signal to come in and not cause interference to someone that'll be annoyed enough to file a report with the FCC. Hell, they'll do it just to keep the competition out.
That said, it hasn't stopped people from trying. If you go to the FCC CDBS and search on FM Translator applications in MA with a status date between Jan.1, 2003 and Dec.31, 2003...you'll find 21 applications that are "received" from the Great Translator Invasion of 2003. They're still sitting there, waiting for the FCC to act on them.