I think we should hold off speculating what attractions Fantastic Beasts lends itself to. We don't have a book to go on to know which locations the first movie uses or where it's inevitable sequels will be set. Obviously the first movie is set in 1924 in New York City. Iconic locations from the trailers or stories on Pottermore would include MACUSA (Magical Congress of the United States of America) and the American Wizarding School located in Massachusetts, Ilvermorny. The director and the production designer have made statements that allude to the fact that the sequels will span the globe. I think it would be wise for Universal Creative to hold off on any Fantastic Beasts development until it's trilogy is completed, or at least the third one is in pre-production so they could get an idea of what will happen.
As far as Potter goes, I think that both Islands and USF already have enough of the IP represented. Other than my hope of an eventual Ministry of Magic ride overtaking the Fear Factor plot, any more would just be overkill in either park. However, since Potter is obviously a huge draw and a cash cow, I believe the wise move would be to save anything Fantastic Beasts to be a main anchor in a third Park.