But really, relicensing a GPL codebase to MIT is uninteresting.
Let's do the interesting one, which is: vibe code a "clean room" reimplementation of an entire proprietary codebase! After all, Microsoft released a "shared source" proprietary version of Windows. Now try seeing what happens if you run THAT through the "turn it into public domain" machine
Win-win outcome, no matter how it goes
Winning option 1: yes, you can vibe code proprietary codebases into the public domain, allowing us to bootstrap proprietary codebases quickly
Winning option 2: stopping laundering of copyleft codebases
Either of these are interesting outcomes!

With customers ask whether they can use Microsoft’s Copilot services without worrying about copyright claims, we are providing a straightforward answer: yes, you can, and if you are challenged on copyright grounds, we will assume responsibility for the potential legal risks involved.