I like your discovery ideas! In fact, administration load is already a factor on how large polities can grown (though it's kinda buggy right now) so something like bureaucracies and infrastructure (roads, cities) will be needed for polities to grow bigger. The only drawback is that both discoveries depend on having a basic economic model, which the game doesn't currently have. So more steps are needed before I get to implement these.
Colonial administration I think would work better once I get to implement more complex forms of governments beyond tribes. For example, colonial administration would be great to form maritime empires. Though that's not so far of. I think I'll be dealing with some form of imperial administration in version 0.3.4 or 0.3.5.