I can only imagine that the only way to scale that would to make whoever owns the repo responsible for automation as well. A dedicated team can provide the tool

I can only imagine that the only way to scale that would to make whoever owns the repo responsible for automation as well. A dedicated team can provide the tooling/frameworks (basically a "golden path") but if/how would need to be up to the team. I think in a general sense this is the approach Netflix takes to services. That said I have no idea how Netflix does source control, only that they use BitBucket/Stash on-prem and that supports both mercurial and git.