Inside Google this is apparently the norm, with lots of tooling to support https://acawiki.org/Why_Google_Stores_Billions_of_Lines_of_Code_in_a_Single_Repository ... probably happens to lesser extent within many organizations, but Google's huge scale makes it seem more relevant/aspirational for worldwide FLOSS, or that's how it strikes me. I don't know that practice has been studied at all, but also feels to me like should be usual.