"a new train song or a new version of one might thus get disseminated pretty rapidly"

It's a fact that people who learned folk music used trains. The pursuit of regionalism (I never have heard what that pursuit's supposed to be for) may not fit great with that fact, but they did.

Some lyrics about people traveling on trains:
"The train got my honey and gone" -- John Lowry Goree, born about 1881 in Alabama
"That passenger train got ways just like a man/Steal away your girl and don't care where she land" -- Floyd Canada, born about 1887 in Texas
"I caught that Frisco, she was fairly flying/I was on my way to see that darling girl of mine" -- J.D. Suggs, born about 1887 in Mississippi
"When I leave I'm going to leave on the cannon ball" -- Lasses White, born in about 1888 in Texas
"I hate the train, train that carried my baby away..." -- Frank Stokes, born in the 1880s or 1870s in Mississippi or Tennessee

In early blues music, "going" from one place to another, traveling quite a distance (e.g. "going where the chilly winds don't blow" or "going down the river 'fore long"), was an extremely common theme, because people did.