It would be a bad idea for them to put Harry Potter in a third park. The way they have it setup now is brilliant w/ the hog warts express- it's smart and it works perfect. Putting a potter attraction anywhere else would be sloppy and not make sense on how you get there.
At this point- they have two options- build next to DA or build next to hogsmeade.
Fear factor or disaster! Go for it- let's make a ministry of magic. Telephone booths can take you there, and you can do a flume ride or MOM battle, etc.
For IOA- take out sinbad and add the forbidden Forest that connects to hogsmeade.
Those are just my armchair ideas.