Yeah, the Mass Central as a pressure relief valve of sorts is not really thrilling me. Sorry.
The section I'm really very concerned about is Worcester - Springfield, which comes after where you'd rejoin the B&A anyway. Between Worcester and Framingham there's plenty of room to 4-track, and Framingham on has enough density of commuter rail stops that 3-tracking and getting creative with some station adjustments should be enough to allow for overtakes of commuter rail by the faster trains.
And, continuing my being perfectly honest, forcing everyone en route to Montreal from Boston to board a westbound train and transfer to MTL HSR at Albany-Rensselaer is really the ideal solution if we can't / decide not to get a dedicated ROW like Lowell - Stony Brook Branch built up to spec.
No need to apologize. It's just a half-baked idea, not my firstborn.
I apologize for misunderstanding you; I had thought you were concerned about WOR-BBY, since you talked about having to tear up half of Framingham and Newton to accomodate 4 tracks, so I was trying to come up with ideas on how to bypass those areas. (I enjoy thinking through stuff like that, even if it involves, or even is limited to, pie-in-the-sky ideas.) WOR-SPG, I have no idea about, but I definitely agree that the Mass Central is not the solution for that.
I think I'm pretty much with you on having to transfer to go BOS-MTL at high speed. As much as I love Boston, Montreal and high speed rail, the three of them together right now does not make sense to me. So many other things should happen before that.