"This morning, we sat down to talk Green Lantern," Guggenheim told MTV, "and we ended up riffing for an hour and a half on another, much more obscure character. Sometimes, you just have to roll with it when inspiration strikes, you know? I'm sure the studio wouldn't be happy about it, but we're not going to blow the deadline. We'll get it in."
Guggenheim said that he and fellow screenwriters Michael Green and Greg Berlanti (who's also directing the film) are on the third studio draft, and they've just been refining the script based on studio notes and locations.
"[The changes are] nothing that's affecting the storyline, really," he said. "It's pretty well set. But sometimes we'll move a scene to a different location for budget purposes, perhaps in an already established location instead of a new one. It's a question of, which locations can we live without? It's a constant process to streamline what you're going through, even after the film is shot, when you're cutting things in the edit. That's what the rewrite process is like, how you sand down the roughness of the a movie to its smoothest."
Besides scripting, Berlanti is in constant talks with the designers such as Aaron Sims (who recently gave us a peek at his "X-Men Origins: Magneto" character designs).
"I'll come over and drool [at the designs]," Guggenheim said. "I will say that the design work is truly mindblowing, and it's hard to pick a favorite. But the shots on Oa are spectacular. What Oa looks like has never been seen on film."
And while there's already a lot of speculation over who would play Green Lantern -- Ryan Gosling? Matthew Settle? David Boreanaz? -- what about Clark Kent, who will make a small cameo? Will the part go to someone already established on film or television to be the Man of Steel, like Brandon Routh or Tom Welling?
"There were rumors that Tom Welling would have a cameo in 'Batman Begins' as a young Clark Kent, to meet up with a young Bruce Wayne," Guggenheim noted. "But you have to be careful when you do things like that, because it sounds great in concept, but when you sit down to watch it, it poses the danger of pulling you out of the film."
But as a self-proclaimed "sucker for a good Easter egg," Guggenheim said, "The fanboy in me would love that. Robert Downey, Jr. in 'The Hulk' was awesome. I love that stuff in general, and I think the fans would enjoy it. Brandon Routh or even Tom Welling [in 'Green Lantern'] would be awesome. And anything is possible. The beauty part of being the writer, though, is that I don't actually have to make that judgment call."
For more on the film, be sure to check out our chat with Guggenheim about the comics that inspired his "Green Lantern" screenplay here on Splash Page, too! Who do you think would be good for parts in "Green Lantern"?