If there will be a GrapheneOS image for the Pixel 11 without MTE, could that open the door for GrapheneOS on a lot more phones that support AOSP?
It would be inconsistent to require Motorola to provide MTE support and then to support the Pixel 11 without it.
There are no phones directly supported by AOSP. Motorola is helping us support their devices and port our features to them. We have to do an immense amount of work on it ourselves for Pixels and already did a lot of it for the Pixel 11 devices. Other devices are missing more than MTE.
Regarding direct AOSP support, there are many devices that work fine with just the generic system image, which I'd count as direct AOSP support.
I believe nothing prevents other individuals and organisations from building what you're suggesting with GrapheneOS code and ideas.