Or perhaps the bitcoin devs could simply create a new protocol to invalidate or permanently lock up ancient wallet addresses that were made under the original less secure system of addressing,
which would not effect the more secure SHA-256 wallet addresses in use today. Just an idea, don't know if that could actually work or not.
It's technically possible. But it definitely will receive lots of critic and maybe even hostile response. And FWIW, the dev should lock address where it's public key is known which isn't really related with SHA-256.