Earlier quoted context omitted.
Couldn't Google use an immutable HAL as a way to make updates themselves? Let users drop manufacturer customizations and get stock android on an older phone.
They might. In an edit above, I remarked that for such a system to exist indeed Project Treble is a necessity. But taking centralized control over the way Android updates will be a very ballsy political move by Google to make. Some smaller vendors might appreciate that these responsibilities are taken away from them. Sony, HMD/Nokia and Lenovo/Motorola are basically only adding some apps, themes and tweaks to AOSP at…
I think this is an issue for Google when they want to introduce new platform features for developers, e.g. Project Tango. If updates take years to get to users, it handicaps Google's ability to be innovative.