It seems like Amtrak is going to stick with the "round trip" type of operation and also understand the appeal of rare mileage. If the trip stays based in Philly I would look to a Trenton Line, Lehigh Line, Reading Line, Harrisburg Line circuit.
The High Line was clearly the highlight of the trip and allowed Amtrak to get back in darkness and still provide value. Next year they could do a similar move, heading up the High Line then making a right turn at Falls Jct to use the Trenton Line to CP-WOOD (or if SEPTA can move that Blueliner they could use the Royal Blue connection and head out SEPTA). Using the West Trenton line would allow for some real Passenger Train Speeds as well as go through authentic fall foliage territory.
At Bound Brook they get onto the Lehigh Line and follow that back through Easton and Allentown and Reading to Philly.