> If it's already turning into a rewrite, how feasible would it be to adopt Brett's `py` launcher?

I looked at it already, and I'd have to write literally the same code to implement what's needed :) (as well as learning Rust and convincing everyone to let us use Rust in CPython...). Practically nothing can be reused - there's no registry, no shebang handling, and our process launching on Windows is already very complex (and has to remain that way for compatibility).

For now, the old launcher will remain to be used for venv redirectors, but I've got the setup in the new one to be able to play the same role, as well as potentially being able to be a script or .pyz launcher with a simple rename.

If Brett's proposal for extensions (other executables on PATH that know how to identify Python installs) happens, we'll probably copy it, though PEP 514 covers Windows adequately (and the rewrite allows non-PythonCore installs to be found/launched). But the codebase itself isn't helpful.