I would love to see Michael Keaton star in another Batman movie. I know that I am not the first person to voice this opinion. Keaton is currently in the midst of a career renaissance. Now would be a perfect time for Keaton to enter The Batcave again.
Imagine Keaton as a mature Bruce Wayne/Batman. There are two ways to go about a storyline. Either adapt Frank Miller’s iconic The Dark Knight Returns. Or write an entirely new story. In The Dark Knight Returns Alfred somehow manges to live on and continue to assist an aged Batman. Imagine a story where Alfred has passed on and Bruce Wayne/Batman is truly alone for the first time. Does he go on alone, or find a new butler/partner/confidant? Does he find young new heroes to mentor? The possibilities are endless.
Somehow convincing Michelle Pfeiffer to reprise her role as Selina Kyle/Catwoman would be a major bonus. Without Alfred Batman loses focus and begins to cross the line. He becomes an extremely brutal avenging vigilante. Catwoman, his one true love interest, helps to bring him back to his original mission.
Every actor since Michael Keaton to portray Batman has brought something different to the role. Of all of the post-Keaton Batmen, Ben Affleck is my favorite. He brought a physicality to the role that the others lacked. Overall I feel his somber portrayal of Bruce Wayne to be the best of all of the actors. That said, Michael Keaton remains my favorite Batman. Seeing him portray an aged and gritty Dark Knight would be amazing.