I just played a few siege matches for the first time. I really like the idea of it, but it felt like I didn't really make any kind of difference in the match, especially when it came to trying to control the AA battery. Someone in there called it the "grinder", and overall feelings about the match seemed frustrated. Once a battleship launches, everyone in the match is at the same part of the map, and it's essentially just a frenzy, with no real tactics involved on the team level.
But what if there was more than one AA on the map? Defense and capture of the AA batteries would become a more strategic matter, instead of a frenetic, zero-sum mess of bullets and explosives in one place on the map. Identifying which AA needed better defense, or which was weaker for the taking would make things more complex and (I think) fun. Plus it would probably cut down on some of the frustration I imagine people may feel in the mode. It would also make it harder for one team to gain a distinct advantage early in the game, as battleships would likely fall faster, and it would make concurrent launches (from each team) less problematic. If it seems the battleships falling too fast, they could always be beefed up too.
Anyway, that's just my idea.