I think New York north of Westechester County and east of the Hudson River should be considered part of New England rather than the Mid-Atlantic. But for the imaginary dotted line that divides NY from CT, VT and MA, you would never know when you had crossed out of New England. The terrain and the biosphere are the same as New England. We have some covered bridges and charming little towns just like New England. We have maple trees and make syrup, and we are as eccentric as any New Englanders.
Why is this important? When devolution happens, I would rather be a subject of New England than of the Mid-Atlantic Federation, but I don't want to have to migrate. Actually, most of upstate New York would probably be content to join New England and have New York City and Long Island split off. New England, upstate New York and the Maritime Provinces of former Canada would make a pretty good realm. I would prefer a Constitutional monarchy under one of Queen Elizabeth's spare descendants, but I suppose I will have to content myself with a Republic.
I predict that the Mid-Atlantic Federation will be marked by a strong central state and crushing taxation and many of the same divisions that plague the unwieldy United States. Pennsylvania, for instance, has been described as Philly and Pittsburgh with Mississippi in between. North and South Jersey are pretty different as are the various parts of Maryland and Virginia. The solution would be further devolution, of course, but I predict that the various states will be leary of going it alone.