Is this not the happy medium Google is trying to hit?
Power users can unlock their bootloader and do whatever they want. This is still officially supported, with vendor blobs officially provided.
By default things are restricted to deliver a happy user experience in the context of the average person that just wants a product that works. But you're free to do whatever you want. There's (usually) even controls to remove restrictions from apps manually without doing the custom ROM route, but there is always the ultimate power user toggle there of "flash a custom ROM"