I’m not sure if this was already suggested but, what about the ability to modify cars further than to just place metal plates, generators and cagelights on them like in 3.0, for instance we could have engine upgradeable parts that come in airdrops and such.
Maybe a system like this:
Engine Parts, Dedicated Armor Plating for that specific car: Very Hard To Find. (Depending on the type of car) These plates would perfectly fit onto the doors of vehicles like an extra layer, they wouldn’t be too op, just able to withstand small calibar ammunitions, and could then be able to craft/upgrade these plates to withstand larger calibers, but maybe not explosives? (For balance)
Bulletproof Window replacements: Slightly Less harder to find, maybe more compatible with a wider group type of vehicles. (Like Civilian Vehicles only, and maybe other types of window replacements for other types of cars e.g. Industrial get bars over the window so they can’t be smashed easily, this has plenty of room for better idea’s)
Then maybe more cosmetical type of upgrades: Spoilers, Better exhausts, More headlights (They’d be more flush instead of putting on cagelights in 3.0) types of tires (Offroad, Sport, or Normal)
As a side note, maybe with the 1 seater, 4 seater and 6 seater constructable vehicles in 3.0, 4.0 could allow better customization of those said vehicles, like we could take body parts off other vehicles that have maybe blown up or been significantly damaged beyond repair and make our own type of car with those said body parts, allowing better customization instead of pile of plates, a chassis, 4 whiles and 4 seats. (For a rough idea if you know a game called Crossout, quiet fun, its a similear idea to that, maybe even have the ability to modify and mount player controlled weapons on larger vehicles)
This won’t be an easy thing to implement I think , so Nelson would most likely take his time to do more important features before something like this. This type of suggestion could have many possibilities, maybe not the way how I depict it but its an idea.
Always open to suggestions on this idea 