hey,
A track builder / editor would certainly be something that we can look into. I know the game 'Chivalry: Medieval Warfare' released their mod tools earlier this year i think. they also based their game on Unreal3. So it can be done
Also we would be looking into ways to allow you guys to paint up your own cars. There's nothing quite like wearing your own tags while stealing fastest lap.
Any more info from the community would be greatly appreciated at this time while we are bouncing around ideas for this project. If it comes to anything we'll be sure to keep you guys involved and suck you dry of all your ideas