Was one of my biggest wishes for GT6.
Custom huds for all viewports (besides premium interiors).
And not just rearview mirrors. But being able to chose between "analog speedometer" and a "digital" one.
Same with rev counter.
Including the placing of (and not just on/off)
I would really like the option to have the rear view mirror from bumper cam available in all views. Some cars have a fantastic roof view but without any mirrors it's very difficult to race cleanly so I never use it.
I would love the option to remove the damn rear view in full screen mode. It knocks off a few frames per second. In replays you can disable it in full screen mode and the game runs at 60 far more often with less tearing too. I think they could tweak the arrows that show when another car is close to have a bit of a further detection range to make up for the mirror.