I just thought of a flaw with the hard mode idea.
It is going to be difficult to do it with a different car than was initially set with the challenge. unless you ONLY do the challenge with the "hard mode" vehicle. Otherwise everyone is going to have to post so many different screenshots due to leader boards taking only the fastest time into consideration. I think it is a very cool and novel idea, but still think keep it plain and simple might be the best. For the organizer as well as the drivers. Just my opinion