Maybe i've posted this here before, but perhaps
this map may be of some use to folks here?
It is called "Greater New Jersey Railroads" but actually depicts all the lines around Boston, including everything south of Portland ME (the author is still finishing all the Maine routes)
EDIT: been thinking about the comments on the last page, about an "all-state MBTA" type of organization. I thought I'd write a little bit about the rail organization I'm most directly familiar with, JR East in eastern Japan (since that's where I'm living right now!) JR East is an interesting example since it's by any American standard extremely well-run, and maybe we can see where what they do is impossible to achieve in MA (or: how we can achieve it!)
A few points to consider: JR East owns almost all their rails; they have been running their local lines basically continuously for ~100 years; many of those local lines are operationally unprofitable; the state paid for electrification and double-tracking decades ago, and still runs freight on those lines; shinkansen lines are mostly operationally profitable, and they run on dedicated tracks (of a different gauge). I think a fine stand-in for Worcester might be
Takasaki station on the Joetsu line. It's the last real commuter stop for Tokyo-based trains,
and 220km to the north is Niigata, which is roughly the same distance as Worcester is from Albany NY. Tokyo-bound
trains from Takasaki run about 3~4tph, except in the early morning rush hour when 7~8 trains leave. In the opposite direction,
there is an hourly train to Minakami but north of that, the
trains run once every two hours to Nagaoka, still an hour away by local train to Niigata. From what I can tell, two trains run this basically bouncing back and forth. Also, Tokyo and Niigata are much larger, respectively, than Boston and Albany.
In a JR East world, which on this forum is somewhere between a crazy transit pitch and "if you were god mode", MBTA could run a local train between Worcester and Springfield with local stops in, like, Ludlow, Palmer, and Brookfield in under 2 hours. Running that one train every two hours means you need two trains for operations. Since Springfield is bigger and closer to anything north of Takasaki, you could probably run 1~2 rush hour "super express" trains to Boston as well. You could also probably get away with a local train between Springfield and Pittsfield making the same hyper-local stops, likely two trains bouncing back and forth every two hours. This could also work for Albany-Pittsfield, perhaps. But it barely works in Japan, on a line through a massive mountain range (ie: harder to drive) with already-existing infrastructure investment and much larger, more dense settlements along the line.
So imagine double-track & electrification between Albany and Worcester, an investment which would *need* to be useful for the freight operators otherwise it'll never be close to worth the investment, and those freight operations would need to be tightly scheduled to keep places open for regular passenger service. If you manage that you might be able to have local service outside current MBTA territory. In that case, electrifying New Haven-Greenfield is also worth it, since that line will have far higher commuter traffic than anything east or west. This is not even getting into the issue of HSR on the corridor, which I've assumed writing this would be two new tracks in tunnels and viaducts. Perhaps that assumption is pure god-mode territory.