It's entirely possible, and repositories like https://github.com/facebook/fbthrift/ https://github.com/facebook/fbthrift/ are an example of an open source proje

It's entirely possible, and repositories like https://github.com/facebook/fbthrift/ https://github.com/facebook/fbthrift/ are an example of an open source project that is synced commit for commit with a private monorepo. It just requires some tooling (like everything with monorepos)