You would want an xtensa llvm back end first. The biggest issue I think would be the lack of available ram. Micropython is written from scratch to be very focus

You would want an xtensa llvm back end first. The biggest issue I think would be the lack of available ram. Micropython is written from scratch to be very focussed on being very small and uses a simplistic trace garbage collector whereas swift uses reference counting that tends to need more ram and more CPU. Possible but unlikely to be practical.