My favorite possible solution to this problem is "spacechains," explained here: https://www.youtube.com/watch?v=UY8CDEpg5_U Relies on OP_CTV, which will likely be up for speedy trial after Taproot activates in November. You can read more about OP_CTV here: https://utxos.org/ Another interesting, and also controversial proposal for a sidechain where some kind of stablecoin could be implemented is here: https://www.drivechain.info/

Lots of possibilities, the future is bright--but I am very skeptical of RSK and Stacks at this time--I honestly feel like it needs to survive about 5-10 years to prove it's stability and potential. Not familiar with Echo, I'll have to look into that.