I'd like to see blind spot indicators come back. It's a huge reason why online races are so messy.
That is what this red bubble is. It starts small when the car is a few feet away and gets bigger as you get closer to a car.
Overall I am happy with what I have seen. It looks like a logical progression for Gran Turismo, and to me it will be the best one yet.
To me one of the coolest new features to the franchise is the Multi-Function menu while racing, to adjust fuel map, brake balance, ABS, TCS, etc. They did this in a really elegant way, and it will be interesting to see if they add more adjustability in this menu over time. And hopefully they make it less obtrusive than it is now.
I can't wait to see how well they pull of night with headlights and rain/snow (they list snow tires after all).
I think they are doing really well with the sounds in general, but as others have mentioned the transmission whine in some cars almost entirely mutes the engine noise. Most noticeable to me is the 458. Outside the car the engine note is good, and in replays, so I think they just need to re-work the sound mixing on some cars.
I would like to see the option to arrange/hide certain UI elements, it is certainly obtrusive right now.
And lastly, I would really like to see the ability to move the driver seat camera position up/down/fwd/back. I like to be able to clearly see the rear view mirror and driver side mirror at all times, and being able to see the passenger mirror by quickly glancing the camera to the right.