My 2018 prediction is that a terror attack (or other high profile event, say a massive human trafficking ring bust) of some sort will get blamed on "Bitcoin financing" and this will be used as pretext to go after one or more US exchangers and seize assets. That's why - never keep your coins on an exchange-controlled wallet. If this happens, it will take many years if you ever see your coins again. By then the worldwide crackdown on exchangers will crash the Bitcoin price, so it might not matter at that point.
