Does anyone have experience putting their production branches in a separate repo from their development branches?

GitHub makes it very easy to make a pull request from one repo into another.

This would seem to have a lot of benefits: you can have different branch protection rules in the different repos, different secrets.

Would it be a pain in the ass?

For an open source project you could have an open contribution model, but then only allow core maintainers to have write access in the production repo to trigger a release. Or maybe even make it completely private.