I think it’s reasonable to say Deep Forest, and any other originals, could be coming soon. The argument for originals coming back to GTS was strengthened with the addition of one of the former paid dlc tracks, not to mention the sheer length of this track means that they probably got one of the heavy hitters out of the way in terms of detail. Knowing PD, though, it will once again come from left field and nobody will expect it.
In terms of cars, anything could be added really. The Supra NASCAR seems likely due to how much PD was promoting the Supra road car/race car, especially since we are close to the start of the NASCAR season. Other notables could be the M8 GTE, 488 GT, Ford GT GTE, etc. due to IMSA and the Rolex 24. Something out of left field will probably be another Pebble beach/SEMA winner.