[vvvrrooomm]

IMO the solution is git submodules. The problem with submodules mostly is the horrible workflow and the missing tool integration. Varying dependencies could result in separate parent repos that contain different subsets of submodules. A simple script can fix tooling: first commit the submodule changes then create the parent repo commit.

[qznc]

You don't want to create a commit in the parent repo all the time. If you fix a typo in a comment in a submodule, why commit anything to parent? Anyways, which parent, since there can be many. There should be more than one. Otherwise why use a submodule?

Another problem is that one forgets to update submodules when switching branches. Afaik git does not do this because of possible data loss in submodules?

I like submodules in general. They are great for dependencies where you want to follow more closely than release version. Still, it would be even easier in a monorepo. The main reason is probably that every anti-dependency is visible.