Marvel boss man Kevin Feige confirmed the news in a casual way while talking toabout the new villains of the Marvel-verse:
No big deal, they can get pretty much whoever they want for these roles now. Although Keaton did appear to drop out of the film last year before coming back on board. Maybe he was a bit wary about getting back into this comic book world.
You'll see him face off against young Tom Holland as a teenage Peter Parker when Homecoming hits cinemas in summer 2017.