Very realistic as Dark universe, The Wizarding World of Harry Potter – Ministry of Magic and SNW are not composed of one singular IP. SNW features nintendo properties (yoshi, donkey kong and mario kart), MOM is composed of the potter series and fantastic beast (2 separate IPs) and Dark Universe features monster movie where Universal has been the production company of. So, really only Berk is the one singular IP land.
I am also kinda on the fence about a Sci-fi based land as celestial park is kinda space/science based with the astrology aspect and whimsical nature so it would kinda feel like more of the same. Any new portal will have to have a strong , out of this world feeling like all the other lands. I personally feel if they did use Oz/wicked they could create a visual masterpiece of a land to rival the other 4. Since Illumination and Dreamworks are out, I cannot think of another franchise/brand that has multiple IPs under it's umbrella that would be suitable to use as a portal.