> Trying to turn that back to rail would be the hardest NIMBY battle in history.

Yeah I didn't say it would be easy, and that's why I mentioned having an alternative bikeway via Mass Ave bike lanes. Some of which already exist but aren't protected.

> Rail trails aren’t really made to create bike paths, they’re made to ensure trains don’t come back.

No. They're meant to do a number of things:

• better utilize an underutilized public space. no different from putting a park on a town/city owned parking lot that isn't used fully.
• create cycling routes to provide an alternative commute/travel option. this can actually improve traffic in some cases (see this bloomberg article with examples of bike lanes in NYC)
• land bank the space so it can be reactivated a rail corridor later on. specifically in the case of the Minute Man the MBTA still owns the land and leases it to the towns which it passes through. the majority of rail trails I'm aware of do something similar, where the State leases the land on a long term basis (99 years or whatever) but adds a clause that they'll take it back if needed. the bike to the sea trail has this kind of setup as well.

In this case, with the MBTA owning the land it's just a matter of the State government having some balls and providing residents with alternative routes and improvements to please them. Ultimately if the State wants to, they can just bulldoze the path and throw down some rails. See this recent thread on how they did that with Logan, or how they almost did that with the Inner Belt and definitely did so with the Pike and 93.