Honestly, I don't like the idea of this being a dancer. It's too similar to monk and would add yet another melee dps to the mix when we're still lacking a variety of other class types. I know that Yoshi P heavily alluded to RDM with his Scarlet Witch shit, and I can't see them basically confirming dancer as a class as well before the other two fanfests. Personally I think the trailer just depicts two MNKs.

It's important to remember that this is a cinematic and is therefore not completely representative of what's in game. Just because she uses some moves that MNKs don't, it doesn't automatically make her a new class. It's also been said that we are going to meet this NPC in the near future - and as we know, NPCs don't often follow the rules imposed on us as players in game. We also have no idea how the classes we currently have will be evolving from lvl 60 to 70 - it's very possible that MNKs more get some skills that are more fluid, as shown in the trailer.

Don't get me wrong, I'm all for dancer, and people are free to speculate and believe what they will. I just hope it's vastly different from MNK, and not like what we see in this trailer.