Interestingly, we discussed something similar, but not quite the same in the Infrastructure meeting today:
TL;DR: we want to re-structure the repos in a way that while katello will retain its own versioning, you will get the “correct” katello by fetching foreman/X.Y/katello repo (and foreman will be foreman/X.Y/foreman, and plugins foreman/X.Y/plugins).
Would that suit your proposal too?