This is assuming the character in the trailer is indeed a dancer.
Their fighting style seems awfully similar to Monk's. From what I can see, they're fast paced, blunt damage mixed with possible slashing damage.

I know it's premature to base things like this off a trailer, but it has me worried that we're about to get another Bard/MCH scenario where either Monk outclasses Dancer or Dancer outclases Monk.

Or it could be the dream and we synergize greatly with eachother, but I have a feeling SE wouldn't, it would make taking one automatically mean taking the other.