For 3rd Rail, they are currently showing the ALCO FA-1 A and B coming up soon, but do not list the FA-1 in PRR colors. Granted, the Pennsy only had 4 FA-1 ABBA sets, but still it seems like they should do the Pennsy FA-1 in as delivered colors.
They did the PRR EMD F3 Phase 2 Late with the correct bullet number boards. How about a F3 Phase 3 or Phase 4 with the correct bullet number boards. Or even a F7 Phase 1a with the bullet numbers boards before it went to the large number boards.
A FM H20-44 road switcher would be nice. The PRR, NYC, and UP as well as others had this engine.
A Baldwin VO-660/DS 4-4-660 switcher. These were used by a whole bunch of railroads.
For GGD, I would like to see some head end or express cars. Specifically REA pre-big red diamond (pre-1954). Troop sleepers would be great since a lot of current models have zinc pest or other issues. No billboard reefers. Or maybe a crew express cabin car (rider car) used by some roads.
------------------------------------------
Now, if they really want my money they need to make steam: Either a N2sa (Standard USRA 2-10-2 for non-Pennsy folks and modified to PRR), a B8a 0-6-0T tank engine, or K2sa/K3 4-6-2 just because they look neat.