It sounds like you know more than I do, Milwaukeeroad.

I hadn't a clue that Thomaston had a roundhouse, or that there was a siding there. Perhaps I'll get up there with a camera this weekend.
Haven't heard anything new about Yellow Dog, but I doubt it'll go forward with the economic slowdown - copper just isn't priced high enough anymore, and there's a fairly organized movement against it opening. Same with restarting White Pine Mine, let alone any of the Keweenaw native-ore mines. As for the South Shore ROW, at least the half from Nestoria to Sidnaw still has rails, out of service and only used for car storage. West of there, I don't think it's even officially railbanked, just in use as the snowmobile trail, and even if CN owned the property outright you'd have some issues moving the trail and repairing the grade. If Yellow Dog went through it'd be a worthy expense, but almost certainly not otherwise.
Ah, now I see what you're saying about the line and a shortline operator. (see
here for the Wisconsin rail map in PDF)
Progressive Rail already operates the old C&NW from Rice Lake through Cameron to Chippewa Falls, and they've been very aggressive in finding customers around the Twin Cities. Perhaps they could put in a bid and take over the White Pine-Prentice line as well as the Soo main from Tomahawk to Prentice to Cameron. Either PGR or another company might convince shippers in northern Wisconsin and the western UP to leave trucks... doesn't seem like CN has tried very hard there recently, since they apparently think the ex-Soo is worth more as car storage than it would be as active rail. Hopefully that'll change.