Timm started with Warner Bros. Animation in 1989, and was the chief shepherd who guided Batman: The Animated Series and the entire DC Animated universe into existence as we know it.
He's apparently been planning to head out for a while, according to an exclusive over at Voices From Krypton. There are worse swan songs than The Dark Knight Returns, of all things.
The Supervising Producer job is going to Justice League/Legion of Superheroes/Batman: Brave and the Bold veteran James Tucker:
“I’d love to use more of a variety of characters, but that’s something I don’t have control over,” he says. “Granted Dark Knight Returns was long overdue to be adapted and I’m glad they did it and did it superbly. But beyond that, I’m not really interested in replicating, image by image, word for word, something that was in a comic book, because you can’t replicate that experience or feeling. You’re basically getting a secondary experience, so you have to make it your own in order to make it work as a movie. Creating films in which people are going through it with a checklist saying, ‘Okay, they took that out, they took that out…” I’m not interested in doing anything like that.”
Tucker is very sharp on the risks and needs involved in branching out in ways that I wish WB/DC's live-action production people would understand:
“Our challenge,” he continues, “is that people want us to do these other characters, but if they don’t sell that threatens the whole line. So the way to do it is to be smart. If we know we’re going to use Superman, Batman and the Justice League, how do we use them as gateways to these other characters? If Batman, Superman and Justice League bring in the average person who’s not a comic book fan, once you have them you insert a Huntress or a secondary character like Oracle as a means of introducing them to more of the world. But you’re not going to be able to do an Oracle movie. Unfortunately the Green Lantern and Wonder Woman movies didn’t perform like we would have liked them to, even though I thought they were among the best we’ve done.”
This is the right guy to take the reins from Timm, and at the right time.
If Disney/Marvel isn't already circling Timm to do work on some combination of Star Wars and, in my mind, overhauling Marvel animation, they're nuts. Hell, WB would be crazy not to engage him to oversee, fix, and guide their expanded DC Live-Action Movieverse. Everyone start backing up Brinks trucks.
Looks like this is not entirely accurate, as reported by DC Animation "Super PR Guy" Gary Miereneau to The RealmCast, as dug up by my pal Ryan Gallagher at CriterionCast.