wather and damage definetly, cars are the least problem actually, there is already alot of cars in the game.
Then throw in some weather with the ability to "change" so that suddenly in the middle of a race rain starts pouring down. Then also add nightdriving, and a complete 24h day with changing weather conditions. It will never make the game boring, and the endurance racing will never be the same.
However, LFS is in desperate need of new rallycross tracks... there is a huge number of racingtracks as there is, and the rallyX only have a total of 6 tracks in you throw in the reverse ones aswell...