There are a lot of things I don't like, but few so far that I would request PD change. Here is what I would ask to change, because I assume will stay the same in final game otherwise:
1. The time taken from when you're put behind the wheel of your car to when the race starts is too short in Sport mode. I like to dial in certain settings for launch in the MFD sometimes, and I'm getting no time to do it. GT6 quick match gave you a lot of time (probably too much.)
2. Tone down transmission whine generally, turn up the engine sound in-cabin. Some cars seem worse than others.
3. Livelier force feedback. Just.. do whatever Kunos does with AC. Thanks!
4. Add an in-car view of dashboard w/o wheel.
5. TC less pulse-like and intrusive at lower settings.
6. Tiny tire temperature band around tread wear indicators should be thicker. Do they even matter? See #7.
7. Tire condition/temperature complexity. For when tire wear is enabled, I expect tire abuse to actually matter. In GT6, managing tires only mattered in long races where abuse resulted in faster tire wear. Someone running racing soft should see odd tire behavior after 3 or 4 laps of constantly overdriving the tires on an average twisty circuit. I'm not expecting AC-level complexity. I think this has a place in GT.
8. In sport mode, the screen displaying the winner of the event is a great touch. I think it should show 3rd, then 2nd, then the winner. I am a sucker for glory.
These are things I suspect might be addressed in the final game, eventually, but will still list the here with optimism:
9. Driving view customization, like seat position and FOV.
10. Some level of HUD customization, though I do plan on sticking with the "all information" view they give us by default.
11. Options for whether it alerts you of your SR level going up or down. I'd rather not know what the net change in SR was until after the race. Seeing that has become distracting and an unneeded frustration. If you wanted to know when/where/why SR change happened, it could show in replay.
12. I'll mention engine sounds here. They're improved for sure, but PD can always do better.
Anything else I don't like would be a more general characteristic of Gran Turismo that I wouldn't expect to change:
13. Physics. I feel like the game is really forgiving in a way that translates into inadequate punishment for sloppy driving behavior. The fastest, cleanest guys will always win, but the game does a lot of enabling. Why I wouldn't change it? Because it makes the game way more accessible for controller users. Go play AC on a controller. I wouldn't expect anyone to deal with that. As long as the physics can't be taken advantage of to go faster by driving some weird way, it's all good.
14. Tire squeal. It can seem a little excessive, but I think it has a well thought out purpose as supplemental information for the driver, who (particularly when using a controller) can not receive the important grip information from the tires otherwise.
Lastly, I haven't run into a single bug yet. There are official channels for bug reporting and forum-style discussion, though I don't have access to the latter.