I believe that the primary market for coreboot is x86, and will be for a very long time (possibly for ever).
I, on the other hand, believe the embedded market is a lot bigger. Pretty much every embedded board uses its own coreboot equivalent -- well, not equivalent, we really want coreboot to not be riddled with bugs, and it to be flexible and user-friendly, and packed with features and all that goodness.
You are welome to prove me wrong,
Don't worry, I will. Ooh, a challenge! :-)
Segher