Is this a joke? Are they trolling us? Or is Blizzard finally delivering on the Dance Studio promise? It most likely is just a fun addition to the UI mock-up. But it's fun to speculate.
Update: Yup! Just trolling us. A+ trolling Blizzard, please troll again. J. Allen Brack said on the live stream interview: "We talked about and developed a whole bunch of different animations and different technology that we could use. We didn't really come up with a really great game system behind it. It is something that we talked about. It is something that we wanna do at some point. But it's not something we're currently working on."