I love your game mechanics so much, and this is a smart way to bring players together. The mechanics and narrative make sense.
But like our off-campus critic said players are now all pressing one button and all doing the same thing. Wouldn't it be better for one player to walk and one to complete the quest.
I also expect your game to have different levels. You guys could reuse a track, but the speed of the black fog that may advance behind you on the track, including the difficulty of the co-op missions, is different. Otherwise it might get a bit boring doing the same thing all the time on a long track.
I think this assignment is still in a prototype stage at the moment, but with a little improvement this could definitely be a great game.