According to CVG, two trademarks filed by Guitar Hero publisher, Activision, have recently popped up on the US Patent and Trademark office website. The two names, Guitar Villain and Drum Villain, are linked to "computer game software" and "games sold with electronic guitars," both apt descriptors of everyone's favorite couch-jumping rock sim franchise.
Though these trademarks could simply represent a move by Activision to protect their brand from similarly titled knock-offs (eg. Instrument Protagonist), a diversification of the brand seems more likely, especially with Neversoft getting involved with the main series. There's still that mysterious port on the Xbox 360's X-plorer guitar to consider, not to mention the possibilities (and dire need) of a drumming game on the Wii. Keep your eyes and ears open.