Oh cool! Would you be willing to contribute that to the editables project (assuming it does work 
) I couldn’t find a way that implemented all of the required semantics.
The key problem is that PEP 420 requires that changes to the filesystem while the Python process is running must be picked up. There’s an example in the PEP here, and I’m pretty sure I wasn’t able to make that work with a meta_path hook.
I agree this is an obscure case. I’ve no idea whether it’s acceptable to break it for editable installs. In editables I chose to document that it didn’t work and let the caller (backend) decide which trade-off they preferred.