THR is reporting that Jackman and Fox are currently negotiating for Wolverine to appear in the film, though in what capacity remains unseen. Based on who has joined the cast already, it seems likely that Jackman's involvement would reach well beyond a vulgar-ridden cameo appearance.
In X-Men: First Class, Jackman's brief cameo helped tie the prequel to the X-Men Trilogy and offered the first meeting between Charlies Xavier (James McAvoy) and Logan. The sequel will also feature McAvoy along with at least three other classmates from First Class: Michael Fassbender (Magneto), Jennifer Lawrence (Mystique) and Nicholas Hoult (Beast).
Where Days of Future Past takes a new turn for the X-Men Cinematic franchise is in the introduction of time travel. The Wolverine we will likely see could be from the future and part of a contingent that already includes Ian McKellen and Patrick Stewart reprising their roles as Magento and Professor X, respectively.
In the Days of Future Past comic storyline that the film is likely at least influenced by, the future is a bleak place where mutants have been rounded up and kept in concentration camps while giant Sentinels, or robots, walk the streets and enforce the law. X-Men from the future travel back in time to help stop that future from occurring.
Hugh Jackman has already wrapped up shooting The Wolverine, the sequel to X-Men Origins: Wolverine that arrives on July 26, 2013.
Bryan Singer is directing X-Men: Days of Future Past and begins shooting early next year. The film will be released theatrically on July 18, 2014.