The Virtual 24h of LeMans really showed how much a damage model would help immersion. And I don't mean just damage caused by physical collisions. I mean it would be more immersive for all racing, but especially endurance racing, to have a damage and failure model similar to what flight sims have where there could be specific problems with the hardware or software of your race car which could cause you to be in the pits trying to diagnose it and fix it.
For endurance racing, to not include this is as part of the simulation is pretty unrealistic. Creeping damage would be great too, where if you rear-end another car during the start, maybe the radiator doesn't fail for another few laps. Or maybe there is fender damage that takes down your tire during braking or high speed or some body move that interacts with the tire. Or for the car you rear-end, they have damage to their headers which crack and cause an oil fire which, if caught in the pits, could be salvaged after an hour of repair, or which could end your race in a fireball if out on the circuit.
I think a lot of this could be simulated based on random chance, especially the electrical problems. But the errors need to be interactive so you're not just sitting in the pits looking at a progress bar. It could be an AI driven race engineer similar to ACC's race engineer who asks you questions about how the car was handling before the failure and then recommends fixes.
Or you could play as the driver and the engineer where you need to figure out the software issue. Maybe there's a loose ground wire that overheats your battery and then suddenly lose all electrical power. So you're back in the pits and the problem goes away, so you go back out and lose all electrics again. But after a few minutes, the car starts back up. So you come into the pits and an engineer finds the problem and you're back out onto the track and into the qualifying/race session, but now you're at a disadvantage.
How cool would an endurance sim be in multiplayer if one of the players is just playing as the pit crew/race engineer and the other is playing as the driver, and they switch half way through the race.
I feel like if you can simulate tire temps and damage across a tire, and if you can simulate oil pressure, water temp, brake duct size affecting both brake temps and aero, etc, then a lot of these things can be simulated right now with the right plugin running in the background (like in AC).