My take on this, is before they will be phased out if ever they will, it will take long before such scenario will happen.
There are few jurisdictions that may be strict towards these privacy coins.
However, if the crypto exchange is registered in a country or place where the regulations in crypto are not that strict, they can still enjoy their presence.
There are purposes why a lot of crypto users like the use of privacy coins, and I don't think these coins will be gone very soon.
They existed for so long already, and they may find a way how to go around these government regulations.