I actually built this as a startup two years ago. There's quite a few "prediction market" website out there which can be both for karma and real money. We tried

I actually built this as a startup two years ago. There's quite a few "prediction market" website out there which can be both for karma and real money. We tried to combine predictions with social media to allow users to build authority. The hard scale problem here is the reputation of the artibers of the challenge. We ended up pivoting when we realized to make this compelling at scale we'd essentially become a news site, and we didn't want to do that.