As far as I'm aware as an outsider, the aim is a device that is compatible with GrapheneOS like the Pixels, yes.
>If you're thinking of devices shipping with it, would this fix the issue of Play Integrity/SafetyNet failing?
I think to pass this you need to be 'blessed by Google' which means being certified Android by their standards. GrapheneOS have mentioned that their CTS/CDD Android certification process holds back some of the privacy/security features (think things like new Sensors and Internet permissions etc.) implemented so they cannot can't target it.