Where cross-gen will hold it back is the amount of cars on track. It being cross-gen rules out multi-class endurance events with 200 cars on track. The yearly Nurburgring 24 hour race won't be possible if it has to keep parity with the ps4 version. The PS5 should be able to handle AI for 200 cars, ps4 likely can't. GT Sport already had a bit of trouble with 20 car standing race starts. (Fine with rolling starts, but too many cars too close together had fps dips, on ps4 pro)
My ultimate race: 24 hours, 200 cars, multi-class, dynamic time + weather, perhaps with shifts for online (co-op taking turns) or save and continue in the pit for off-line, will likely have to wait until next gen or next next gen. One day it will come! 100 player battle royale is standard nowadays, time for racing to catch up!