It will never happen. Cryptocurreny will be here to exist until there are traders on the on exchange. The government doesn't have that much authority on banning privacy coins especially if the coin provide a lot of advantages or usage. The only time that the government can intervene is when crypto is not following the law or affecting the money circulation.
In any case, the world is already brewing up a situation where cryptocurrency should not be recognized as securities and assets. Cryptocurrency must maintain such status so as not to attract the attention of regulatory authorities. Although if we take into account the capitalization of the entire cryptocurrency market, then such money will always attract the views of the authorities.