Massachusetts
This is what's left of the original Massachusetts once we scoop off the Boston area.
The Boston-area state should be called Massachusetts because the Massachusett nation lived in what's now the Boston area. Not sure what this state should be called.
(Scott Brown would probably have survived in 2012, for example, although he wouldn't have had the opportunity to run in a special election to begin with since Ted Kennedy wouldn't have represented the state).
Ted Kennedy
could have represented this state since he lived in Cape Cod rather than Boston for much of his life (and indeed died there). I agree that a hypothetical #entrenched Scott Brown probably would have survived 2012 with this electorate, although I definitely don't think he would have survived 2018.
Local Government: The Governor is basically a coin flip. On the one hand, removing the most Democratic part of the state would obviously favor Republicans, but on the other hand, removing Boston might take away a lot of the animus that powers Republican campaigns in the state.
Statewide Republican campaigns here aren't really anti-Boston; if they were then maybe the Pioneer Valley would vote Republican in statewide campaigns. Charlie Baker has been much more of a shameless handmaiden to the Boston area and its economic interests than any of his opponents. Remember that Gonzalez wanted to debate Baker throughout the state but Baker insisted on debating in Boston and only Boston.
Capital: Yonkers is the most populous city, but it's too far South and too close to NYC to be acceptable to the majority of residents. There is no obvious choice aside from it, but I think Poughkeepsie would work decently.
Poughkeepsie is a great choice! It has a distinct local identity, some cultural particulars (Vassar College, etc.), and pretty good transport links. Well-chosen.
Capital: As mentioned, Albany and Syracuse are by far the largest cities. Unfortunately, they're also both far off-center. My guess is that they'd split the difference and go with Utica.
Why? Albany is just as off-center in the actually-existing New York State of which it's been the capital for centuries as it is in this state, albeit not on the east-west axis. And its transport links to the North Country are way better than those of any Central New York city.
Great work for the most part. These are mostly just nitpicks regarding terminology; the rest of what you have so far is fine or better than fine. This was a great project to make your 50,000th post.