SEC just charged an exchange operators for probably some pretty exotic tokens "With Operating As Unregistered Broker-Dealers":
https://www.sec.gov/news/press-release/2018-185. If I was an exchange operator I would now diligently check all the traded coins and tokens and stop the trading of all that could be seen as securities. This probably applies not only to US based exchanges if only they let USA citizens to trade on them.
The coins that are interpreted as securities by SEC will be gradually delisted from the exchanges and their price will drop - this might be a good idea for a short.
