I like the ideas of Wicked/Oz and LOTR as park lands but I think both are too redundant with IPs and vibes already in Epic Universe (Harry Potter, How to Train Your Dragon, Dark Universe)...gray stone, castle-esque structures, Euro-centric stories, dragons, wizards.
The Epic expansion needs an IP that brings a totally different milieu to the park, like jungle or old west or ice-scape or futuristic or Asian or pirate. My vote is for a 1960s Tokyo with an "epic" (the biggest show building ever!) action-packed dark ride attraction featuring massive (30-40 foot tall) animatronics of Godzilla, Megalon, Mothra battling it out with fire and lasers and bursts of sparks in a huge model city as we fly around them. Plus the land would have sushi, ramen, a pachinko parlor, cool Japanese merch and an amazing nighttime vibe with neon and illuminated signs. Having a very distinctive land like this will make the park feel bigger.