I have a version of the Revolutions trailer here. Dunno if it's the one you people saw in the movie theaters, but it start with a conversation between Niobe & Ghost. It also ends with a conversation between Niobe & Ghost ;)
I'm not entirely convinced the 'dockwalls' would mean Zion, but I do certainly agree that Zion is still around. I've tried to find Zion-scenes in the trailer (must'a watched it 50 times yesterday

), but I can't seem to find one. Not one with people around anyway.
But just to re-iterate, I believe that Zion is still alive & kicking. My only question is this: the 9 hours that Lock said the machines had left, was that perhaps until they got to the 'ambush/counterattack' point? Or does this statement of 12 hours mean that the walls/roof of Zion are made of something special, and need something special to rip 'em up?