Bitcoin and other Cyrptocurrencies can never become mainstream - as long as we have concepts of nation states.
No govt will ever allow a shadow currency and parallel economy to become the mainstay of their public expediture.
And let's say even if it does happen, anybody who knows about crypto or has info on it, knows this cannot be enforced. I'd say good luck enforcing this. Crypto in nature how it works is just not possible.
And ban on crypto won't get the prices down or create FOMO, whoever has invested, has invested for a long term.