[reanimus]

Where are you seeing devices without Bootguard fused? I'd be very curious to get my hands on some of those...

[transpute]

As a Schrödinger-like property, it may vary by observer and not be publicly documented.. One could start with a commercial product that ships with coreboot, then try to find identical hardware from an upstream ODM. A search for "bootguard" or "coreboot" on servethehome forums, odroid/hardkernel forums, phoronix or even HN, may be helpful.