The Graphene team has seemingly partnered with an OEM, who is releasing binary security patches for them already (with source code available after embargo lifts). Hardware does not seem too far away at this point either.
This is not a reason to sit idly back, of course. GrapheneOS is in danger, as you say - it's just not necessarily from this particular decree.
their days are indeed numbered.
As for not being a certified android device and being unaffected. That is not true. There will be chilling effects that result in much less FOSS app development for Android, and whether or not an OS is certified is irrelevant in that regard.
for a lower bound, check a reasonably popular alternate ROM like: https://wiki.lineageos.org/devices/