... what would/will be the next most promising smart contract platform for the eth-based projects to migrate to?
NEM of course.
Smart contracts are much easier than with ETH.
NEM might have a chance since there is a bunch of Altcoins that like to have the contract thing with their coins. If Ethereum dies then there would be a bunch of coins going down since there's many coins using ETH to help improve their technology. Ethereum won't be better than Bitcoin though.