I have a couple of ideas to throw out there for future tuning challenges. I haven't followed all the previous challenges, so these may have been done already, if so, ignore me...lol.
1. A custom track challenge. I know, most custom tracks suck badly, but I've driven a few and made a few that are excellent tracks, with none of the silly hills and hairpins over the tops of hills type of thing. It would require everyone testing and tuning to friend the person with the track but I think it would add another dimension to things and shake up the formula a bit. It can be done but it would take a bit of planning and a little more lead time than the usual shootout.
2. A no ABS tuning challenge. It seems to be growing in popularity and I think some of the guys into no ABS driving could be encouraged to sign up as test drivers.