Still not excited? Just wait.
Apparently this new project won't be standard Harmonix fare, as the developer is believed to be looking for a narrative designer to add story-based elements to the experience. While we have no idea what they could possibly be planning, their job listing (via Supererogatory) clearly indicates that whatever this supposed new IP is, it's going to be a drastic departure.
"Harmonix seeks an accomplished Narrative Designer to incorporate creative story lines into gameplay on a unique motion-gaming IP," the listing says. There are also listings for a Software Engineer, Senior Content Designer and Senior Level Designer.