Then again, maybe it'll be like Valve's Team Fortress 2. Remember, that game was literally slated to hit stores in 2001 (I remember waiting at Best Buy for it on "launch" day ), and then... no word until 2006, when Valve announced it had undergone a complete makeover.
I'd like to think no work on large-budget titles like these is truly canned. Portions of work done on Ghost could probably be transferred in someway to Starcraft 2.