I'm working on a draft that I'll post soon~ish. I'm stuck on "Why". why as in why why not how,what but why sort of why :) are you doing this?
I can offer this perspective as to why EOMA68 is attractive. To design a device based on a modern full featured SoC/CPU that is capable of running a desktop level OS requires designing a PCB with high speed signalling for the RAM etc. This is a non-trivial task that is beyond most people without specific engineering expertise, and expensive software tools. A modular CPU card like EOMA68 has all the high speed stuff taken care of, and can be dropped into a PCB with a PCMCIA socket that even an advanced hobbyist can design, get manufactured and then populate by hand soldering. As far as I know, there has not really been anything like this in the past.
Making custom or prototype devices with modern CPUs is now accessible to a far wider range of individuals and companies than before, and those devices will be upgradeable as more EOMA68 cards appear.