If I'm interpreting Christian Svensson's PR speak correctly Zack & Wiki fans won't be seeing a sequel anytime soon. Not long ago a leaked retailer list had Z&W2 as an upcoming Capcom game, and some even said that it would be shown at their recent Captivate event, but nothing official has surfaced about the puzzle solving pirate.
Let me preface this answer with a statement to set expectations that we've not announced another Z&W and I'm not so sure there will be one on any reasonable timeline. - Christian Svensson, Capcom
It's understandable that a company would not want to reinvest in a franchise that did mediocre sales, but seeing how Z&W's failure is entirely Capcom's fault I have no sympathy. In spite of the hard puzzles in the game Zack & Wiki was given a kid friendly coat of paint and advertised as a kiddy game in magazines like Nickelodeon. The very weird, unfriendly title didn't do the game any favors either. Add to that the fact that point-and-click puzzle games are a niche, nearly dead genre and you have a recipe for failure.
It's unfortunate as Z&W was an excellent game, but I wouldn't expect a sequel anytime soon. I wouldn't expect the sequel to follow in the first game's footsteps either. They'll probably change the genre and revamp a lot of things making it more of a spiritual successor than a sequel.