Zac Posen was recently on ANTM where the contestents did a runway show for him. He is a super cool guy from what I gather and I am hopeful he is the one doing the dress.
Hollywood Life spoke to Zac and asked him about these rumours:
“I can’t. I don’t speak about any of my projects and the reality of her(sic) non reality.” Well, he may not have said he’s definitely designing the dress, but he did say he doesn’t speak about any of his projects. Before walking away, he added in, “You know I do love a wedding.”
Twilight Lexicon writes:
This is how Stephenie described it, “I wish I still had the picture I based the description of Bella’s dress on, but it was lost in my fateful computer crash. Those of you who are going with the old fashioned look are on the right track. Two key words to aid in the search: art nouveau. It’s a simpler style than the frillier Edwardian stuff. Elegant white satin, cut on the bias, with long sleeves (the strapless thing is a very recent development. It wasn’t even popular when I was getting married, only 13 years ago, much less during the modest turn of the century). I search google images for the dress every now and then. I’ll let you know if I find something close one of these days.”
You can see some sketches and ideas of possible designs on Lexicon.