The railroad operates too many trains to safely operate railbike tours on sections of track that are part of their regular excursions. If the railroad ever decides to offer up this kind of service, I think the Redstone Branch would make the most sense, trains don't regularly go down it, it offers up some of the best scenery they have to offer, along side Pudding Pond and the grade doesn't seem all that bad. If (and I mean if) the wanted to offer different length tours, they could probably work out a lease with the state to go further east, just for the railbikes. Aside for cutting back the brush east of the Saco River bridge, there would be little to no track maintenance required.
It takes real skill to choke on air, fall up the stairs and trip over nothing. I have those skills.