Server-based multiplayer like Minecraft, since BeamNG is already very supportive of mods. Servers can be private or public, for friends or with community hosted race challenges. This could be expanded to a legitimate rank system experience for tightly controlled races or challenges where players can climb up a leader board. It would be cool to see who the best drifter or best rally racer etc. of the country is.
not possible with current technology. There are no less than 400 results for searching on multiplayer, search before creating threads