Nicholson had played roles (The Shining, One Flew Over the Cuckoo's Nest) where he could pull off the crazy Joker role. Keaton I can agree with, but it's not like he did a great job as Bruce Wayne or Batman (despite what Maxim magazine thinks).
Ben Affleck could pull off Bruce Wayne, but it'll be hard after Bale played it so well.
To be fair, later in the article (the page is a jumbled mess) it says
So that explains the youth movement. The movie is still going to suck though.The story of the film will reportedly be more based on the Ultimate Fantastic Four comic book than the series that launched in 1961. In the newer book, the team forms at a much younger age, with a teleportation experiment being the impetus of their powers, rather than a botched space shuttle flight.