With all this foresight it's necessary to build parallel rails. If merchant adoption raises substantially they will just make it KYC. They want to get rid of cash and they fight non KYC cryptocurrency use.
And as long as they have power they will enforce anything that keeps it that way.
In my opinion it's a waste of time building solutions for the status quowhen the trajectory is more than clear.
Think about merchants who want to opt-out. What do they need? How would they do it? That'll be the real market!