I think it would be interesting if there was an AI that would go all-out on one strategy, but switch course mid-game to focus on something else. e.g., start out as an Aggressor, but then start fortifying, or vice versa. Obviously it would take some work to make sure that it didn't switch at a bad time, though... ideal would be if it could figure out when a good time was! ("ok, my fortifications and defensive fleet just destroyed the main enemy fleet -- time to assemble a strike force and zap a planet or two...")