Anyone consider allied selections that use models and fluff that integrate them into their main FOC? For example. I have Chaos Marines counted as Blood Angels..... but was looking for a way to use converted beastmen as Kroot and some kind of flying cyborg champion as a battlesuited HQ to add firepower.
In my case I'm not pushing FOC boundaries (like taking allies for 4 Heavy selections etc) But I feel it gives me more Codex options that remove the "Allies" theme.
What other options can you think of? I can Imagine DE-Eldar being role-reversed to expand options in their own codexes.