Wizard has published a great interview in which Brian Michael Bendis asked Joss Whedon questions about a variety of subjects. The Wonder Woman came up:
WHEDON: I am having enormous trouble with the ["Wonder Woman" movie] script. It’s going very well and I’m loving life, but because it’s only at script stage and there will be no discussion of casting before, I don’t really deal with that. No, it’s weird, I’m in my office and it’s just me.
WHEDON: It’s kept me busy for a long time. I’m finally finishing the second draft. I’m very happy with it, but wow! Wow, this one was like pulling teeth. It’s tough. I would watch “Batman Begins” and just grumble, just b*tch and moan, because he’s got everything. He’s got so much of the work done for him. He’s got the best rogues’ gallery. He’s got the best origin story. Wonder Woman is a lot more to figure out. But it’s coming together.
You can read the full interview at the link above.