This sounds like the wrong solution to me. The problem isn't (or rather, is rarely[1]) that you've "polluted" a public branch with bad code. Bad code gets pushed into branches by perfectly legal commits all the time, and you fix it via software engineering and not administrative policy.

The real problem with the accidental force push is that it's lossy. The OLD head, to which you would hope to revert when you realize your mistake, is suddenly invisible (and garbage-collectible!).

So I'd much prefer to see github fix this with a "hard reflog" of the branch state on the server. Track the head of each branch at each point in "monotonic server time" (with a tag or whatnot, or even outside the repository would be fine) such that you can always (1) detect force push events like this and (2) trivially revert them.

[1] Yeah, occasionally you might push your site keys, or some NDA-covered source code. And in those situations you want the reverting push to actually "forget" the code. But that should be the rare exception and not the standard process.