Suggestion:
For starters, we should really consider
dumping the idea of adding necrons, eldar, deldar, tyranids and tau to the mod
for the moment. We simply don't have enough units for them. When units for them arise, I think we can consider these "civs".
Or, we do have some for tau (hammerhead & firewarrior by smoking mirror), but I think there are none for d/eldar/necrons, and tyranids are just weird.
And let us concentrate on what really can be done (imperial guard, space marine chapters, witch & daemonhunters, chaos marines and orkz. and somethings I might forget).
Sorta like what embryodead/mr.do/mrtn did with WHFB-mod - adding things afterwards. You might hate this idea, but it's an option, not an ordnance