It does seem rather odd that they'd sort of "tease" this co-op concept without implementing it in some form or fashion. That brief clip is fairly contextual...lady goes on to say "what is this? co-op? Then you join the arena where 6 others are waiting which is an important way to introduce the multiplayer..." (paraphrased)
Still it makes one wonder if that bit of a tease will be foolishly overlooked by the developers...Co-op is a huge and largely untapped arena in multiplayer gaming. It's scary to think that we've ZERO about a potential co-op mode in this game...but SSM has managed to stay hush-hush about the ENTIRE game for the entirety of its development so hopefully this is just that one last reveal waiting to happen to throw everyone's excitement into a fever pitch before release...?
Omg Co-op would easily get this game game of the year. its just to danm good at that point. Multiplayer, Online Co-op survivor, and epic single player and nothing will touch this game. That footage easily shows that it is possible.
I really do wish there is co-op. Like Tank_610 said another multiplayer game mode is just a variation of "kill people". Team favor is pretty much Domination and King of the Hill combined, or seperated depending on the maps. Co-Op would indeed be awesome.
On a side note, some of the dev videos pretty much confirmed AI grunts (Satyrs, Gorgons, etc) in multiplayer. Whether this means an actual co-op mode or just AI in the maps is something we'll have to wait to find out.
HOWEVER, based on the footage it seems that the secret mode is a co-op/versus hybrid where you can't directly kill your opponents but use the environment to prevent them from completing the objective, which is to kill as many monsters as possible.