I can see this happening:
-They expand HP in the Jaws location, and build a Hogwarts Express in between new and old.
- When visitors enter one of the parks to see the Harry Potter stuff, and then board the train to see the rest - they find out that they can only get on the train with a ticket upgrade to a "two-park" pass.
Basically by spreading HP across two parks they force people to buy a more expensive ticket if they want to see it all in one day. Scumbag move, but marketing genius!