Ah, thanks for clarifying.  So which of these is the main thing you really want:

1. reload extension modules
2. completely restart Python

It sounds like #1.  If that's the case then there are a number of issues to resolve to make it work.  However, there are some serious technical challenges to overcome. :/

So if it's #1 the problem space is relatively focused so a solution (if possible) would be tractable in the "short" term, so it *could* happen. :)  However, if it's #2 then a lot of things will have to fixed and so realistically it might never happen.

FYI, either way none of it will be backported, so the functionality would not be available on Python 3.7 or earlier.

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FWIW, in VS Code they run their plugins (extensions) in a separate process.  Their docs give some insight into plugin system design. :)

   https://code.visualstudio.com/docs/extensionAPI/patterns-and-principles#_stability-extension-isolation