I have a feeling they're weaning us off of EMH and will be introducing special FP+ perks to onsite guests.
I'm going to UO/IOA for the first time in August...you can buy a pass that will get you express line access for one time per ride for the day, the price depends on how crowded they expect to be. The more crowded, the more expensive, but the more you need it.
However, if you stay onsite with them, you get an unlimited express pass that gets you onto any ride that uses it (most of them) as much as you want all day long... No waiting for windows to open or timing your FP around your meal....
Don't you think people would stay on site for a similar perk at WDW?