I love silly discussions about 40k lore. Probably one of my favorite settings.

Part of the appeal is the universe is so large you can always pick some random part of the materium and say on THAT place, stuff is more on your liking. Perhaps there is no chaos influence, or perhaps Tau and Imperium have a long-lasting alliance...

Or you could just go vanilla and focus on the canon lore.

Everything goes as long as there is only war.