It would be The Walking Dead all over again if they brought the Potterverse into Halloween Horror Nights. They'd race to cash in, and the soul of both HHN and Harry Potter would be lost. At least the target audience for The Walking Dead overlaps with that of HHN; if they did a Potter-themed HHN show, on the other hand, they'd have to either tone it down (and the rest of the event, for that matter) to accommodate the parents with kids, or face a furious outcry from such. J. K. Rowling probably knows this, too, hence why Potter and HHN haven't met before. (Remember the wrangling they had to do with Audrey Geisel for Boo-Ville at Islands of Fear?) I say that the current strategy is the best: leave Diagon Alley open during the event (it's a good crowd sink, after all), but do nothing else.
Anybody think that they might move the Academy of Villains show to the former Bill & Ted space, with the new show put on in the current AoV space? Given the popularity of the AoV show, I wouldn't be surprised if they moved it to a bigger arena.