> My dream is to be able to drop a repo inside another repo and have git just treat it as if it were part of the parent repo. And then to be able to bundle the child repo to the parent and push it.
I'm not sure if I understand you right, but I think I made what you describe: https://github.com/feluxe/gitsub
It's a simple wrapper around git, that allows nested git repositories, with almost no overhead.
I use it for a private library (the parent-repo), which itself contains modules (the child-repos) that I open sourced on github. It works fine for my use case. I wrote it, because I found "submodule" and "subtree" too complicated. 'gitsub' is still in alpha.