Every hardware partner they've (Graphene) reached out to thus far has either flaked out on them or were found to be providing a solution deemed insufficient in regards to security.
One day there will be a Graphene phone, and that will be the day I stop buying Pixels; using stock Googledroid on my 9 Pro currently, originally out of necessity due to getting my older 6 Pro fixed for data recovery, now out of desire to run through the freebies before switching over.
Losing Face Unlock is going to suck hard though.