Bloodmoon for Morrowind involved Hircine heavily; we practically did go to his Hunting Grounds already. I don't think we'll see that Daedric Realm for a while. Everyone also wants to go to the Shivering Isles again, but I doubt that will happen anytime soon either, because there are other Daedric Princes that we haven't had much contact with. Vaermina's Quagmire is my assumption for the next Daedric Realm we visit. There's a lot they could do with that.
Okay, so fair enough on Bloodmoon already focusing so much on Hircine.
The Quagmire sounds interesting on paper but would be damn near impossible to do just from the descriptio of the place. Same would apply to Mephala's Web. Hermaeus Mora's Apocrypha would be boring since it is an endless library filled with books (very cool for characters playing mages/bards/scholars but not a very good idea for a gameplay area). Peryite's Pits are almost identical to Mehrunes Dagon's Deadlands which is basically where we spent a third of our time in the previous game and The Shivering Isles is where we spent the other third.
Malacath's Ashpit would be cool but for it to work we would need levitation or some other sort of flight added to the game. Coldharbor would be cool but might spark too many complaints of "Fallout rip-off" from fans that are not too big on the lore.
Pretty much all the other realms I have not mentioned have been featured to some extent in previous games (Boethiah's Tournament of Ten Bloods in Oblivion which is pretty much the highlight of going to his/her Realm and Clavicus Vile's realm was already featured in Redguard) and according to lore Nocturnal's Evergloam is accessible through the Battlespire, though I am unsure if that was actually featured in the game itself since Battlespire is the only TES game I haven't played. *phew* so uh...what realms do we have left that Bethesda could still explore that they have not done yet I wonder?
I guess Meridia's Coloured Rooms could offer a huge change in scenery. Sanguine's "One Hundred Thousand Realms" could also provide so many possibilities for interesting level design. Azura's Moonshadow might be cool as well and since there is no recorded case of someone going to Namira's Scuttling Void and no description of what the place is like, Bethesda could actually take that and just go crazy with their design choices.
Did I miss anything?
Sorry for slightly derailing my own topic; I'm a madman for fantasy lore (By the time I quit WoW after 5 years I had pretty much memorized the race/history/everything by heart) and I have been playing TES since it came out in 1994 and I was just a wee gamer so...yeah. I do a ton of over-thinking on game possibilities in my free time
