Personally I am betting on DPOS systems to be the next big thing. DPOS systems will not be as decentralized as current POW or POS systems - but solving the scaling problem will be a huge thing. I think people have not yet realized that DPOS solves that and when it becomes common knowledge they will go boom. Many people will shout about the centralization problems - but nobody will listen to them before the problem becomes evident and that will take some time.