Why not just avoid the entire Secure Boot problem by using Coreboot? Because 
the reason we
have the Secure Boot problem is because Microsoft's Windows 8 certification 
requirements
mean vendors have to ship a UEFI implementation with Secure Boot. You could 
satisfy that
by using Coreboot with a Tiano payload, but it'll still have Secure Boot 
enabled so you
still have the same set of problems. But maybe you could just reflash your 
system with
Coreboot? No, because another part of the requirements states that all firmware 
updates
have to be cryptographically signed now. The only way to reflash will be to 
attach a flash
programmer directly to your motherboard.

So why not just use Coreboot? Because it doesn't help solve this problem in any 
way.