They don't dare split up Philly-Pittsburgh. Another one that they would never split up would be Boston-Montreal, but I'm kind of surprised they didn't try to but the Bruins in with the NYC area teams.
Since they're trying to stick to the time zone basis, the only other option I can really think of that they might have even considered would have been swapping Florida-Tampa for Columbus-Washington. Carolina is the closest team to Florida, so they belong in the same division. Columbus has no true rivalries, so moving them is an issue. The NY-NJ block needs to stay together, so you can't move any of them, just like Pittsburgh-Philly needs to stay together. Washington is the only remaining team that makes sense. They have a long history with Pittsburgh too though.