A little background. The line was discontinued mostly because Septa was taking over public transportation. The other reason is septa did not have a diesel locomotive shop and this would have been the only line requiring a diesel locomotive.
There has been talk of bringing it back for the past 30 or years. All studies from varies parties with no input from NS or Septa. A change of train or motive power will still need to be required since Septa has underground stations for it's regional rail in center city.