I'd say the major thing I'd like is realistic transmissions and assists. In this regard, you wouldn't be able to pick between AT/MT and have it apply to all cars, but rather, it'd be on a car-by-car basis, and would include the ability to map a button for the clutch. You'd be unable to shift manually in say, the Supra A90, but you'd be able to do so in a car that uses a manual, or a sequential manual. Similarly, if a car doesn't come stock with ABS, TCS, and other stuff like being able to control the BB and FM, you'd have to buy a part to do that.
I also think the "look back" button could be replaced with looking around with one of the sticks, which would include the ability to, well, look back if you pulled it all the way towards you. But instead of it "clicking" into a rear view (like it does in GTS), I'd allow the camera to have the whole 360-degrees of movement, if that makes sense.
Also, a rear-view mirror for the hood camera would be fantastic, and I'm quite hopeful that the PS5's additional processing power would offer us a higher chance of getting that feature.