I just completed an easy challenge: 100km (I didn't actually use my own craft) .
I thought it would be great if we could have a global leaderboard of all the times. If the player doesn't have an account or doesn't want to submit their time they don't have to. It could be a window or whatever its called come up when the challenge has been completed asking if they would like to submit that time etc.
What do you guys think. Also feel free to express your interest or add more ideas around this topic of a Leaderboard