This sounds to me a lot like git-subtree combined with automation where commits to the subtree's native repository cause automation to add those commits (with p

This sounds to me a lot like git-subtree combined with automation where commits to the subtree's native repository cause automation to add those commits (with path adjustments) to the super-repo, and vice versa. This keeping both sides always in sync with each other can avoid some of the downsides of git-subtree, but has its own limitations like only working when both sides are owned by the same org, does not allow a subtree that maintains "local patches", etc. If simultaneous pushes to super-repo and child repo occur at the same time, one gets applied and the other gets converted to a pull request (unclear if the server reports error back to the git client, or if the push appears to succeed, but then appears to be force pushed over by the other change, being preserved as a pull request.)