I do imagine it would be awesome to be able to summon a giant sea serpent in water, especially if there were strong naval elements in a game.
I've posted before, but the ranking of my hopes for the next setting is:
1. Hammerfell - my first pick for practical purposes, as I see it as the most exotic location of man that has yet to be explored with modern graphics in the main line of games. I also have always really loved desert areas in videogames, for whatever reason. I see it as a place that has the potential to be very massive, exotic, yet familiar, with a lot of cool landmarks and story potential. It's actually my first pick purely because of all of the factions and story potential.
2. Valenwood - would be my first pick but I'm skeptical of the technical abilities to currently pull it off to where it's as exotic and "out there" as warranted. Has the potential to easily be my favorite region in terms of design, with its beautifully exotic foliage, giant plants and trees, haunted forested parts, etc.
3. Summerset Isles - would be my third pick. I feel like it would be fun to explore the island clusters and a game in a magic-prominent region might mean more emphasis on unique and interesting spells, compared to what we got in Skyrim. I think it would be best reserved for the finale in the Thalmor arc, though.
Black marsh would probably be 4th but I'm not sure how much sense it makes to be able to access the region as a non-Argonian currently. The place sounds more exotic than even Morrowind.
As for High Rock, I'm not a fan of it purely because it seems miniscule in size (something the next TES game needs to have an increase in, IMO) and it also seems as if it could perhaps be a bit too generic, although certain parts of High Rock are certainly very arcane/alien. I'd like to see it as a major DLC for a Hammerfell game, tbh.
Aren't there supposedly daedric ruins in High Rock, also?