I'd say that creates a huge conflict of interest.
That's one of the big reasons why Nokia Series60 didn't take off as a licensed OS: Whatever Samsung or LG or Lenovo wanted to build on that platform to differentiate, they had to involve Nokia during the development (who then developed the needed OS-feature in parallel to the Nokia product that will make use of it).
Google is either very secure that their grip on all these HW-vendors is strong enough forcing them to stay, or they are no longer part of Google's long-term strategy for Android.