Need to read this more carefully, but…
…immediately clear to me that I would like to see the buster-developers repository added there too. If resources allow also all the other repositories, buster-testers and buster (stable).
If I am somehow notified that a change in the developers repository breaks something - the challenge here is that there are many different version combinations (also TemplateBasedVM vs standalone vs DispVM etc.) - then of course I will fix that first. Upload a fixed package to the developers repository. And never migrate any broken package (combination) to any other repository.