a little off topic now, but this policy is how we ended up with the SE-0346 nightmare. in the end i've seen people hiking toolchain requirements to 5.7 across the board to workaround the issue which was exactly the worst case scenario some of us warned about after it was accepted.
i think we would all be a lot better off if swift evolution started taking the package ecosystem's existence into account, the compiler does not exist in a vacuum.