I don't see the WWoHP open during HHN for two main reasons. The first is wands. Their biggest money maker in the wizarding world is Ollivanders and wand sales. But HHN has a strict "nothing that can be used as a weapon" policy. What does Ollivanders sell? Foot-long pointy sticks. You wouldn't be allowed to bring it inside the park and if you bought one in the park, you'd have to do package pick-up. That means, of course, that the interactive windows are a no-go, which is a big part of why people buy the wands in the first place.