Adam Hughes has been, since before the All-Star line was even announced, meant to be doing a 6-issue Batman arc with Geoff Johns. That was scuppered for a 6-issue Wonder Woman arc with Jeph Loeb.
However, as I say, this was before the All-Star line was announced.
No work was ever done, and Adam continued with his covers.
However, a couple of months back Adam finished signing a contract with DC and he is doing a full comic book series (I'm not sure how many issues) but he has not stated what the series is.
Since the last thing he said he should be working on is Wonder Woman, people have assumed that All-Star Wonder Woman is what he's working on, which makes senses considering the timing - he did a preview poster for the WW film and the series should be ready for release when the film is getting ready to come out however there is still the question of the Batman story, which Adam did many sketches for, and also the fact that a lot of time has passed since his "I'm doing Wonder Woman" to his current contract and it's very conceivable that it's another project.
Adam doesn't want to say what it is because he doesn't want it hyped or talked about to death. Wise man.
So yes, the popular rumour is Adam Hughes (maybe Jeph Loeb, please no) will be doing All-Star Wonder Woman, but the facts are that Adam Hughes is signed up to do a series which he's working on, but we don't know what it is.
That's the full story.
Personally, I wish he was doing an issue of Solo. I would want that more than anything else ever.