that one -- Edward Woo uncovered some interesting news after sifting through an Activision SEC filing this week. According to the filing (via Gamespot), the company plans to launch Guitar Hero: Metallica in Fiscal 2009, which, for Activision, is anytime between now and March 31, 2009.
No other details are known about the game other than its existence. Will it be guitar-only or multi-instrumental a la the upcoming Guitar Hero World Tour? Regardless, we're guessing that long-awaited new single won't debut on Rock Band anymore.