Harmonix will announce a new game tomorrow, but it's probably not what you think:
Harmonix is announcing a new game tomorrow (it’s not @rockband or @dance_central). Stay tuned for the exciting news!June 3, 2013
The rhythm game developer is expanding its wheelhouse, but it's kept quiet about its new efforts so far. The only clue we have is an August job listing for a combat designer from the company, who would "design and tune combat skills and abilities; overseeing creation of robust combat AI systems for minor and major combat encounters."
That position may or may not be for the game in question, but fighting with fists/guns/lasers instead of plastic instruments or jaunty dance moves would be a change of pace for the studio (if not the industry).