There has always been a few things I have thought about relating to this topic.
Passport checks, why not give us the ability to physically have a passport in game that gets stamped at the border like when you fly in real life you get your passport stamped in each new country you visit.
When you have fatigue turned on, why not have the ability to feed or let your driver have a drink while driving (Real Life Simulation).
When fueling your truck, allow the player to exit the cab of the truck and walk to the pump, give us a button to interact that then put the fuel pump into the tank to fuel the truck for a bit more added realism. You could make it so the shops at the fuel stations can actually allow you to walk inside them to purchase snacks etc
The ability for the windows in the trucks to actually get dirty so you need to spray wiper fluid and use the windscreen wipers more often to clean the windscreen.
On the online servers, make it so that the speed cameras and red light offenses are actually working to actually make people drive to the road rules, might result in less crashes in some areas as people like to just speed through red lights etc so actually adding some sort of meaning to the in-game currency might make drivers actually be more careful in game finally.
Added ability to actually check load stability and that tie down straps are actually applied to cargo before leaving a depot.
Few other things but brain fade atm causing me not to remember all of them.