BlackBerry hasn't been OEM for their last few phones - the KeyOne, 2LE, and 2 were all outsourced to TCL, who is still making handsets. This would also fit with BlackBerry's security image, and even pull in the OnwardMobility vapourware.
I'm every bit as skeptical as you are, and in no universe is BlackBerry the OEM in question, but I would like to live in my delusion until GrapheneOS proves me wrong - I want a keyboard, dammit!
I don't think that there is any need to restart a new category. Just make your new phones good enough for GrapheneOS.
GrapheneOS has close to half a million users, I think it's worth doing some adjustments.