It will probably not happen I think this really would not be good. All new project try not to be called as security and design their currency regarding this issue, so I don't expect big crisis.
I think it's very likely to happen. The SEC has already unofficially said that it views all ICOs as securities. Coinbase released an index fund and poloniex taken over by circle indicates that they are moving towards a more regulated, securitized environment.
What does this mean for the average investor holding tokens bought in an ICO?