Problems would be the number of assets dedicated for one job. For every background music in a zone that you could feasibly fight in, the dancer would need a unique dance. What about leves? They change the background music, does the dancer need all new dances for leve music as well? Plus, some of the major boss fights have really dramatic music that does not really have a particular beat that you could dance to. I think all of these issues combined would make implementation highly unfeasible.