Wouldn't be realistic. Roll cage and 4 and six lug wheels on The LeGran? 6-lugs on the covet? See? BeamNG is supposed to be realistic.
Realistic on how the vehicles move/deform. Plus, theres no rules in real life saying that you cant make your 5 lug car into a 6 lug car, it takes work but its possible
Considering roll cages can be hand crafted.... Yeah i agree on that one. Yes you can change the suspension to make the car take any lugnuts, however i think its kinda pointless. And skid plate...... Why?
Stuff like the wheel hubs is better as a mod, hence why it into one. A big 1.5 plus ton american behemoth like the moonhawk or the roamer, van or pickup do not need 4 lugs and cars like the miramar and hatch definetely do not need 6 lig hubs as the smallest wheels barely even fit in the wheel well. Roll cages though, i think they should be in most cars because like Dr Death said, they are handcrafted and can be built to fit any sort of car. Maybe not for cars like the roamer or van but there is no reason that official rollcages cant be made for the pessima or Legran. Skid plates are not needed. Maybe for the offroader but others do not need them.
Yall are thinking too small. The vehicles are objects that the devs can change any way they want. Theres endless possibilities, and while i think the realism is great, they/anybody can do anything with vehicles, in game and in real life (game is easier tho). Why not have an official vehicle that has a config such as random muscle car mud racer? Or official land speed contenders such as the roadkill bonneville camaro. I feel that the devs are limiting themselves too much when it comes to imaginative, unrestricted, potentially goofy, for the fun of it creation