Let's be honest, that proposal through Maine is juste a pipe dream. It might happen, but it's nowhere near a priority for any of the states it goes through.

However, this corridor might have more momentum then you think it has. Amtrak has already identified the Boston-Concord corridor as a potential corridor to invest in. Mass. is invested in expanding the MBTA and upgrade the lines all over the state. On the other side, New England states have made a top priority to extend the Vermonter to Montreal and double its frequency. Work is on the way for preclearance facilities at Montreal Central Station.

$100M isn't that much, really. If they manage to build enough ridership on each side of that gap, that would repay itselft really quickly. The only serious obtacle would be New Hampshire, which is notoriously opposed to passenger rail.

It might not make sense for Vermont alone, but that Concord to Lebanon line for instance would allow for direct travel from Montreal to Boston, which are much bigger market.