I'm sure it's possible to put that info in README.md and handle things according to that month's donation amount.
I don't know that a GitHub-run tier system will suit everyone, when a developer (the primary users of GH, of course) could easily just automate the update of the relevant info in the README or some other relevant document in the repo on a cadence that suits the project and the developer.
I don't know that a GitHub-run tier system will suit everyone, when a developer (the primary users of GH, of course) could easily just automate the update of the relevant info in the README or some other relevant document in the repo on a cadence that suits the project and the developer.