The fact that the wallet is government-issued does not mean users have to keep the coins in the wallet. Once they receive the $30, they can simply send them to any wallet of their choice.
We will see about that. I personally don't believe that will happen until people in Salvador actually get the bitcoin in that government controlled wallet, and manage to send it elsewhere. Just thinking about Croatian government, if they ever try to so something like that I am sure that they would make shitty custodial wallet, and I don't think that Salvador government is any better, or more capable.
I do hope that I am proved to be wrong about all this, as it would be a giant thing for bitcoin adoption.