stephenie has said right now she has not been in the right mind set to work on midnight sun again and sounds like she may not work on it again anytime soon. if you go to stephenie meyers website and on the home page go down to Nov 16. there is a link to Q and A with stephenie. click on it and go down to the bottom of that page. she makes a statement about what is going on with midnight sun.
Last I heard, she was doing a second Host book and a book about Sirens (mermaids), so I suppose she's a bit busy. She's probably not working on Midnight Sun because it's everywhere & I heard she wants to work on it when people have not heard the word "Twilight" in months, years, etc. She wants to come out with a bang & have people not expect it yet.
So, word of advice, if you want Midnight Sun to come out sooner rather than later, stop talking about Twilight & read other books.