Why is it that all these "analysts" offer opinions about things that they clearly have no knowledge about.
Android is an Open Source operating system. The additional tweaks and apps that manufacturers add on top of it are typically closed source. Google further adds to this across both devices under the Nexus brand as well as any Android device that can run the Google Play Store, with the Google Play Services framework which allows Google to add further closed source stuff on top.
All that Google will do is take AOSP like they are now, and replace most of the AOSP apps with closed source versions (which they pretty much do already).
Why would switching to closed source make any difference to the speed of updates on Nexus devices? Google are already in charge of the update process on Nexus devices, open sourced or not.