The timing of a migration away from dollars will depend mostly on US fiscal and monetary policy. Better financial infrastructure on-chain isn't going to do it alone.

The stablecoins will absolutely accelerate the transition, so that when it does happen, it happens more quickly. Anyone with a stablecoin can transact on-chain for something else. And anyone holding stablecoins will be using an app that has familiarized them with the idea of alternate currencies and currency exchanges.

This is probably a good thing. A realistic not terrible scenario is a few year period where you have to pay attention to exchange rates, but your net-worth is mostly unaffected and at the end of it you're paying for groceries with something that's not USD.