Some friends of mine and I talked about doing one where we wrote bots to manage our teams instead of managing them manually. Then that turned into "We should build a platform that supports that for leagues..." and got lost on beer napkins or something. I still think it'd be fun.
It would be loads of fun. Unfortunately, I think the primary reason why there aren't a lot of cool ideas like this already implemented is for legal reasons. From what I've heard, starting your own fantasy league by using NFL data is just pretty much impossible.
