Commuter train service will not break even if every seat is occupied for every mile. The best case would be to get the subsidy as low as possible. These are not passengers pulled out of a hat -- they're passengers that are redirected onto commuter trains. reducing road and parking congestion by not driving cars or riding buses. So there is a benefit, but a profit is out of the question. The commuter rail agency will need somebody with real knowledge to negotiate with the owner railroad for trackage rights. The railroad will try to gold plate everything on the territory for its own benefit.
In this age, it would be very unwise to attempt to start up a commuter service without Positive Train Control, and especially in view of the well-publicized troubles experienced by other commuter rail lines in New York and New Jersey, as well as the horrible head-on collision in California which got the PTC mandate rolling.
Personally, although I do not pay taxes in Vermont, I think that the proposed commuter service with the ex-Trinity Rail Express RDC's is a good idea, and seems like it might attract a good number of ecology-oriented riders.