Having worked with some organisations building on Android (>1,000 repos), life is not easy when you are trying to build on top of it and regularly take updates etc.
I asked one company how many changes required changes to more than one repo and was told "a small percentage". We then did some basic analysis of issue IDs across commits and discovered that it was in reality nearer 30% of changes. Keeping those together was just plain very hard.
Start to scale this by teams of hundreds or thousands of devs and you get a lot of pain.
Managing branches is also hard - easy to create (with repo tool) - but hard to track changes.
I asked one company how many changes required changes to more than one repo and was told "a small percentage". We then did some basic analysis of issue IDs across commits and discovered that it was in reality nearer 30% of changes. Keeping those together was just plain very hard.
Start to scale this by teams of hundreds or thousands of devs and you get a lot of pain.
Managing branches is also hard - easy to create (with repo tool) - but hard to track changes.