GitHub's beta launched without Pull Requests, but we did have private messages…
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Nowadays everyone already assumes that "pull request" = "web-based code review interface with a button to merge", and I find that unfortunate, but such change of meanings are common and we can only accept them.
But it still makes communication unnecessarily complicated when people have that assumption.
Like, if I host my code with cgit, I bet there's a whole generation of developers that don't even know they can clone my code, host it in their GitHub accounts, and send me a message telling me "hey, I forked your repo, you can pull the commits from my GitHub account if you want".
No need to mess with `git request-pull`, or even email at all.