Single source hardware is a security liability. If Google does something to the hardware or firmware, the GrapheneOS project would be screwed. Google has already hobbled AOSP.
We cannot overly depend on Google’s or any one company’s good will.
I think GrapheneOS should think about gradually steering the project toward a basket of hardware companies. Shifting to Motorola is necessary in the near term, but the whole situation with Google’s behavior needs to be a wake up call.