Whoa...Too fast!
Red51 had an urge to make a fantasy biome so that's something to look forward to, if & when he does it. I also agree that the fantasy biome should assist us in obtaining things that would otherwise clash with the game elsewhere. I'm agreeing it should be where we obtain our floating/flying airship of whatever sort, as with the islands.
I suggest that you folks strongly search up 'Twilight Forest' for Minecraft to learn more about it. I'd love to nudge Red51 into doing a dungeon that would link up with another realm to allow magic, but only in that other realm. We would do realism in the current world while only keeping 'realistic' stuff in such; Likewise with Magic in the fantasy realm.
Lastly, any anime fans here? If you've seen 'Gate' Anime (a 2015 anime), then you'd get the basic idea of where I also want to take this after having loads of fun in Minecraft's 'Twilight Forest' mod. It was fun. I really want to have magic so having an alternate realm to have such would be awesome without clashing with the current. I'd love to have a 'magical' companion (NPC) being able to use magic in that realm while stuck with swords & small firearms in our world.