IMO the cost of building new runways and more taxiways, a whole new set of terminals, buying out neighboring properties, building a highway connection to the airport, building a train connection, and everything else involved would not be even close to worth it to get the land “back” (we never really had that land, the airport is all infill, it was just ocean before.)

I think just building a train to the airport terminals is the best thing to do, and would be a fraction of the cost of relocating the airport. Even just beholding an automated people mover to the terminals and train station wouldn’t be a bad option, and would probably cost less.

As for height restrictions, they really aren’t that significant anywhere other than the seaport. Besides, personally I don’t want Boston to be New York skyscraper dense, I want it to be Paris dense, with more 4-6 story apartments, which are not affected by flight paths at all.