Sounds like the author wants something like Mercurial's https://mercurial.selenic.com/wiki/ChangesetEvolution. It will allow you to rebase and do all kinds of heinous things to your history, but still maintain the original commits that things came from.
Commits are forever. What happens to your history of pull requests if github shuts down or turns evil?
Are there any GitHub clones that record PRs, issues, wikis, etc as commits on separate branches?
GitHub has proven that discussions around code are every bit as important as the code itself, so why not give it first class treatment by storing it in the same medium?