As much as I like the designs of the courses. There's a slight problem.
The only chance the "marbles" can "switch places" is when the starting gate is gone. Otherwise than that they can't really have a chance to change the places. Not ranting or anything, but a race without any chances where marbles can change paths or even places is kinda boring.
I think it's unique on how the elimination method is.
Keep it up!
But one more suggestion. When everyone is sitting down at an elimination area, give some of them different poses. It makes it feel like everyone is different, and just from poses you can see personality, the way they act, the way they feel about some things, ect. But considering this is only in the first stages, I know it'll get much better!