It goes like this:
But what's the point of some aliens having lower standing and less rights when you can't dictate anything at game unless you are happy with it being like Titanic (lifeboats are for rich folks first and they're not stacked) , so more Terran may leave less space for aliens in a "Terran first" fashion.
1) Player can conquer planets, but I don't want the total "wipeout" when a planet changes ownership (since near borders a single planet can go back and forth several times).
2) So, I need the population and infrastructure to survive.
3) Therefore the population has to survive and should be at least partially useful to the conqueror.
4) But I don't want the alien population be as valuable as the original race you started with.
I basicly look for a system where it all would work Grades of citizens and the like is a tool to achieve this, it does not need to be thrilling on its own (but if it's thrilling it's a bonus for sure).
Then , I think conquering a planet may lead to Terranization (or vice versa in case you lost) , if Empire treats aliens less than Terrans, probably aliens will do same for Terrans after all.
So in time demographics may turn in favor or against Terrans, and assuming Terrans are elite citizens they have better life standards and they consume resources more than their population share.
So instead of Empire dictating anything, it's more like a "natural" flow.