As Cosmo said, the G&U formula works down there, because of the proximity to several major cities, close proximity to interchange with an active class I, and the ability to relocate business to help with rising costs of doing business on land in the Boston area. As you pointed out, the G&U has brought in multiple online shippers, and can now take on a few more with the lease of the former CSX line down there. The MD was always more of a bridge route, and never had much for online traffic in its heyday. There are three towns along the entire MD with a population above 10,000 (two being Gorham/Westbrook mentioned above, served by a less than daily local), and if CSRX/NHCR can't be persuaded to handle freight on the active western side (or find it profitable), it would be hard if not unfeasible to simply "bring business in." If it worked, it would already be here. There is simply nothing worth carload potential, or of high enough volume to make it go.
Again, you're ignoring the landscape up here. The proposed pellet mills, or any potential business tabbed for trackside former mill properties, have had the best chance of being potential shippers up here. In the last instance, the pellet operation to be located in the former Simpson Paper Mill in Gilman couldn't even make it to startup due to a lack of subsidized capital to even get the lights on in the place. The idea that someone with deep pockets can simply come in to the North Country and "make businesses appear" is extremely naive. Anything making money up here, is generally going short haul by truck, and not far out of the area.
Avatar: NHV 669 at the south end of the "Pompy" in White River Jct., VT on 4/29/1993. Photo by Richard Roberg.