I think all of your problems are root caused by the phrase "multiple monorepos". This sounds more like "polyrepos" or something, multiple siloed repos that them

I think all of your problems are root caused by the phrase "multiple monorepos". This sounds more like "polyrepos" or something, multiple siloed repos that themselves might contained disparate projects, languages and tooling. Google3 is a true monorepo. 99% of code in the company is one repo, with minor exceptions for certain open source projects and locked down code. Edit: for example, you can change YouTube code, Google Assistant code, a Maps API, some config for how URLs are routed at top level load balancers, etc all in one CL if you really wanted to/needed to.