> "__pypackages__" doesn't seem like a drop-in replacement for virtual environments.
Right, it's not. But if enough people adapt their workflows to use 
[something like] it rather than relying on having a local copy of 
python.exe in order to launch, apps that currently assume that their 
subprocesses don't have their own children would be correct again.

If it was a drop-in replacement, we'd have dropped it in already. All 
the drop in replacements come with similar issues, which is why we need 
to change things more broadly in order to handle all the use cases that 
exist.