On indieWIRE there's a longish Her-centric interview with Spike Jonze, and Rodrigo Perez gets in a question or two about Charlie. That "world leaders" movie? Still, sort of, a maybe-thing:
At one point it was said that you and Charlie Kaufman were going to reteam again in a Dr. Strangelove-esque movie about world leaders. Is that still happening?
It wasn't exactly that, but we do have an idea and I don't know when we're going to do it. I talk to Charlie all the time, we talk about ideas all the time and I tell him what I'm working on and he gives me great ideas and tells me what he's working on. He’s the kind of guy that has so many ideas that are amazing and the next week you’ll be like, “What are you doing with that [idea]?” And he's like, “Oh, I'm over that.” The amount of incredible ideas that either are sitting in his drawer that he's never going to do anything with or that he's forgotten about already; there's so many ideas, he'll forget about and you’ll have to remind him! But anyways, at some point I'm sure we’ll do something together again. He's my favorite writer. (Source)
So that's pretty vague and no cause for people to go all "THE WORLD LEADERS MOVIE THING IS GONNA HAPPEN." But, you know, maybe it will. Some day.
Back in 2011 that project was described as a "satire about how world leaders gather to figure out all the seismic events that will take place in the worlds [sic?], from oil prices to wars that will be waged." Given some of the things Charlie said in his awesome BAFTA screenwriting lecture, I imagine the satire is probably very biting and angry -- good stuff.