I agree that the Keystone Service is like its own commuter service. First, there are many people who live in the more rural parts along the route who commute to jobs in Philadelphia and probably even Harrisburg. As for the future with 125 mph operation on the Keystone Corridor, there is a proposal to have the travel times reduced to a little less than three hours from New York Penn Station to Harrisburg. I would love to see that happen and it would benefit the Pennsylvanians.
Assuming that the Pennsylvanian trains get Chargers, PHL-HBG will be one of the few places in the country that they can max out.
The big hurdles I see are mostly from PHL - PAO. The curve between Overbrook and Merion is brutally slow. Not sure much can even be done.