I believe sense when you get in a vehicle and you automatically hear the engine turn on or when you on a traffic stop and you need to turn it off there should be a way to do that, I believe the following features should be added.
Engine on and off GUI switch
Hazards have a sound to them.
High beams.
These will improve RP and the users experience to the max, adding more realism and much more!
(Now see it would be more laggy, can’t wait for new car features tho!)
gui not necessary as controls wouldn’t be difficult.
hazard sounds would be good, but the lag caused from them may outweigh the benefits they may bring.
people would probably just turn these on all the time and drive around randomly and again the amount of lag produced by them may outweigh the benefits they may bring, depending on how they were made.