First, I don't think Age II can be topped, but if they make it, it should NOT go past the Imperial Age, AoEIII was bad because of the timeline it dealt with, AgeIV should cover either the first's or the second's, or even a combination of both timelines, but not go past it.
Second, they should totally forget what they did in AgeIII, review the mechanics of AgeII and see how can they improve them, but not complicate the game needlessly. The card bonuses, the evolving homebase should not come back. Really, the best way they can make a great AgeIV is to make a perfected AgeII








