There won't be any research mechanism in the Imperium gameplay. I'm not a big fan of research trees in the ancient world (see, e.g., the interview of
Flash of Steel (former Portico), but the main reason is that I do not have the resources (read: time) to add this to the game.
Most of the technological development that occured over our period was small, and changed life relatively little on the scale of the game. The example of the abacus is a good example of this; no doubt it was a help to merchants everywhere, but it didn't make people richer simply for that. With the exception of siege technology (where all the advancements took place in the century prior to Imperium's era) and a little bit of naval development, it is hard to talk of research in this era at all.
The major difference between states, in any case, is the societal systems and culture. Culture broadly determines what kind of troops are available in the state; the structure of the state determines how they can be utilized. And societal structure should be able to change, of course; e.g., if a tribe ends up conquoreing a lot of land, it should eventually develop into a kingdom; same way that the Republic of Rome will eventually develop into an Empire at some point. How these changes and culture interplay is another matter; one which I will probably not get to explore fully at this point (won't have time to implement and test all the ideas).
Keep in mind that - though the total of the game itself may end up pretty complex - I am really working very hard to keep things as simple as possible; lest another 10 years pass before I finish the game (*).

(*) That's an exaggeration, btw; but it sometimes feels like I've been working on this for a decade.
