I would love to get PRR Silverliners and Metroliners. The Silverliners could also be done for SEPTA, but I'm not sure SEPTA would grant a license to do so.
I'd also like to get:
SEPTA Subway/Elevated sets
SEPTA Kawasaki double or single-end LRV
SEPTA Brill Bullet cars
Penn Central, Amtrak Metroliners
Rail Diesel Cars (RDC) sets (any and all roads)