Why would they need to let any additional visitors in when they will have approximately 5000 more people entering the park early than they did in 2010, due to the opening of Cabana Bay with its 1800 rooms? Hogsmeade capacity is presumably 1500. I'm guessing Diagon Alley will double that, which means that the Cabana Bay guests alone will fill both WWOHP sections to capacity and still have 2000 people lined up to get inside.
Things will be very different compared to the 2010 opening. Never again will early entry mean a mere 15 minute wait for a major WWOHP attraction, I suspect.