Anyway, here's how you connect Keybase to GitHub:
https://blog.codefor.cash/2019/08/30/free-automatic-github-b...
https://github.com/codeforcash/github-to-keybase-mirror
Note: this was a v1, and I'm sure there are more resilient ways to do this. Critical feedback strongly encouraged (ideally along with suggestions).
Edit: I can see where your solution has an advantage. When one accepts contributions, all of that can be automated with web hooks via github. Still, having to run lambda/similar for this is a bit heavy weight.
Edit 2: Considering that for a release, I would opt in for release from a tag or explicit commit, that would be a non issue. Pull when needed, for redundancy, use another, self hosted bare repo. Push there in case of github down.
Then, combine that with a git-hook script that designate all non-release branches push to team's Keybase repo as well? Maybe including a custom prefix in the branch name to avoid need for conflict resolution?