This has been in place for a few years and seems to work quite well.
(Google does a lot of creepy stuff, but HN should also give them credit when they do great things)
Quite a few years, means since Android 10, and they add to first introduce GSI[0] (after Treble changes) to actually make it work, as OEMs were free to ignore Treble anyway.
https://source.android.com/docs/core/ota/modular-system
Of course, they could require by contract OEMs to provide updates, like they do for other Google based services.