That siege engine is unmistakable! The fact that it's sharing the same map as the Polish rules out a scenario, so I guess they're as good as confirmed, which is awesome news! I wonder what leader they're going to select? Ashurbanipal seems like a likely candidate both for his military exploits and love of letters. He's also a Grade A Monty-caliber psycho! In addition to the siege engine UU, it's probably reasonable to anticipate a library or garden UB. There are a lot of possibilities for the UA, but my guess is it will treat empire-building, vassalage, or forced population migration in some way. Redistributing population from conquered cities into either raw population or permanent free specialists in your core cities could be a really fun mechanic.