There are two routes to follow with modding.
1) Uncontrolled - We know how that story ends up. Loads of low quality content patched day in day out because 99% of people do not understand they have to ensure quality BEFORE release.
2) Controlled - The person/people responsible to filtering HAVE to make sure NO real life cars/tracks get through WITHOUT full licence otherwise legal issues come into play.
LFS also has LFS world to take into account. Any car track released needs stat logging and hence VERY strict control over when it can be updated etc.
I have played enough games with open modding to know the level of crap that is produced by people that "think they can". So I would prefer controlled and integrated with LFS although that does limit to only fantasy tracks and cars still.