User generated content as competition in game?

How hard would it be to include companies and vehicles created by other players in the campaign?
Maybe once a month or so, you could put out a request for people to upload their cars here, and bundle them all in a small patch that would be completely voluntary to load.
Maybe once a month or so, you could put out a request for people to upload their cars here, and bundle them all in a small patch that would be completely voluntary to load.