[erso]

Your example is incorrect.

If you're the maintainer of wonnage/foo and bar submits a pull request from bar/foo, bar/foo should have been rebased on top of wonnage/foo, not the other way around.

(And if you are in a situation where rebasing on top of bar/foo would actually do anything, that means you have local commits that haven't been pushed to origin, in which case accepting the pull request is dangerous.)