Well frankly I can not imagine what the region would like considering a city the size of DC in between NYC and Philly. Growing up in Bucks County PA I think I am glad this didn't happen, but talk about magalopolis.
Think that would have solidify one contigious urban area in between and interesting to ponder.
That would probably have made for zero comparison on the most powerful/important region in the US.
Basically 3 of the largest US MSAs in an area the size of the Houston metroplex, yuk I am glad I can see great towns like New Hope just outside of New York and Philly, that would have been a mess
Mercer County, NJ | The New National Capital