I'll add onto that tidbit regarding DA's usage..
Actually... the main reason for "No Diagon Alley" last year during HHN was more to do with it being "new" more than anything, so it was used for private events & whatnot. There is usually a lot of private events going on during HHN that are held in IOA, majority of the time in the WWOHP/LC area (if not park wide). So with the new area, its prime private event space, plus you've got Hogwarts Express as well..
In regards to this year, it is rumored that Gringotts WILL be open during HHN (obviously due to crowds). This rumor is due to interesting "express pass" restrictions that didn't exist last year. I have a friend that works at Gringotts who indirectly confirmed the rumor for me by saying that he has already told them he is NOT being scheduled for HHN haha... So we'll see if the rumor does prove true.
okay... now back to our regularly scheduled ooooo-ing & aaahhhh-ing over scaffolding coming down...