Admittedly the Ma & Pa part is more of an experiment than anything. And I was thinking reaching the Philly Docks was part and parcel of the idea for the South Mountain itself.^ Wheeling and Pittsburgh to Easton and Philadelphia....interesting. Definitely a line for bridge traffic over the Appalachians from the NYC and NKP on the west side of the Appalachians to the LV and probably CNJ on the east side at Easton, the Western Maryland at Baltimore (and maybe branching south via Frederick to meet the B&O's junction point at Point of Rocks, thus allowing Washington service?) and presumably somebody else in the Lehigh Valley area. Unless you have access to the docks in Philadelphia I'm not sure what use that line is going to be aside from carrying coal to Philadelphia because the PRR is going to swallow up all of the interchange traffic whole as their route is likely shorter. If you want to use the Ma and Pa route as a freight conduit you'll need to completely rebuild it to deal with the fact that it is as long as it is - the PRR line between the two is over 20 miles shorter even before you get to upgrading. If it were me, I'd dump the Ma and Pa route and build from scratch from York to Baltimore and give the PRR a real run for their money, and make Lancaster a junction point for trains to Wilmington as well as Philadelphia. Do this and then do an interchange deal with the NYC or NKP in Pittsburgh or Wheeling and you're off to the races.
A related note was that I had the idea for it to be split between the NYC and my TL's take on Conrail when the 1970s comes. The NYC gets the lines to Philly and Harrisbueg, and Conrail gets the Harrisburg - Easton line.