@jarkko I feel that it shouldn't be impossible to extend GitHub to provide this experience.
Nothing stopping them from having an mbox http endpoint for each PR, and for the whole repo. Well except maybe perf concerns (AI bots hitting the repo-wide mbox every second). And then per-commit reviews are almost there already — the only missing bit is being unable to comment on the commit message itself.
The value I get out of GitHub is mainly being able to collaborate with normies. You can't get normies to run IRC client 24/7, and you can't get normies to git over email. It's just not possible.
Also, I absolutely hate patch emails. Having each patch be an actual git commit with parents and everything is immensely valuable.