Just something to give people a chance to play various races, and providing a setting so its realistic that they don't all gut each other. Likely allow races like Eldar, SM, Tau. The sort of races that wouldn't....well gut each other. Something like they were all warring on some planet, something massive happened, and they realised that if they didn't work together to save the day they'd all be up shit galaxy without an astropath.
But enough about that, back to your RT game, lets see how this awesome light rule system work.