Pretty straight forward - introduce manual transmission on cars. Could be discutable if only sports cars have this, all cars or even big vehicles (buses, semi trucks). I think it would liven up driving and make it more enjoyable.
+ You wouldnt have to be redlining to go 80 km/h because you could choose your gears.
+ More sense for modding transmission (cuz faster shift speed and more gears for maxing)
+ Better for drifting
+ Better roleplay (as in real life 100% of the population dont drive at 6k rpm)
- Some people could not like it (maybe introduce it as a modification?)
To change gears assign two keys near WASD. For example Z - downshift, X - upshift.