If a largish group of users could create end-to-end encryption not with a single company but with "readily available materials", then stopping it could be harder.
So it's a combination of state dictate and the practical ability of users to defy that. This isn't saying I'm optimistic, I'm rather pessimistic on any ability of a wide home-grown encrypted-messaging milieu to appear - if few are aiming for this, those few can easily be picked-off. But I don't think we should just give up on any part of this.