I would suspect that the sort of person (like myself) that would rather run GrapheneOS over LineageOS would rather install themselves than buy preinstalled. Much easier to verify no one slipped you an altered image.

Verified boot and hardware attestation enable verifying a GrapheneOS install is genuine. It can't prevent all hardware tampering but it provides very strong protection against tampering with any firmware or software.

It takes 10 minutes of clicking "Next" to install GrapheneOS on the pixel. It's the least of the problems.

They problem was always getting a hardware secure by design (like pixels) and with years of firmware updates.

I really wonder which vendor it is, because up until now there was NO alternative to pixels because of lousy hw security. That suggest the big vendor and really great relationship.

It will likely happen after the initial generation with official support. It's hard to do it for the initial generation, but it's possible.