This goes to show where people need to learn about operating system design. At the lowest level, Android uses a Linux kernel, which is where you MUST have driver support for the hardware in the device. Then you have the basic components of Android that sit on top of the Kernel, and then you have the OEM additions/modifications, such as Samsung TouchWiz and HTC Sense. All of this is the really really basic stuff that could be called the VERSION of Android. Everything on top of this is really just apps, even if they are included in Android. Drivers can actually be updated independent of the rest of the OS, so as long as they work, they can be updated. So, VERY VERY modular, and Google could layer it so that the only thing the carriers can really lock down would be those lower layers of the OS, and the rest can be updated directly by Google.
Google Services was the first piece of the puzzle, which can be updated by Google without needing an OS update, and can update or even add features. That is already in Android at this point. If Google goes forward with this idea, virtually all parts of Android could be updated independently of the carrier, and the only things NOT updated by Google would be device drivers, and carrier additions. In essence, you have something that resembles a boot loaded as the ONLY part that carriers would be able to lock in about the operating system, and the rest could be updated by either OEM or Google. That is the sort of thing that first came to mind when the name KitKat was chosen for 4.4, a bunch of pieces that are bound together, but which could be broken off and dealt with individually.