To me it looks like there is an obvious solution: a package should be able to issue an update to change its name.

Something like

- maintainers of package com.foo.pkg want to transfer it to com.bar.pgk

- com.bar creates their own pgk clone and marks it as a successor to com.foo.pkg (with a specific version)

- com.foo.pkg pushes an update with that specific version marked as superseded by com.bar.pgk

- package managers warn users at update time that a change in namespace happened and ask for consent

This could be extended to multiple forks to let the user choose

I feel it would work fine