Where do you think the series will go in terms of story?
In general, would like to see a greater emphasis on character development and narrative. Keep the open-world emphasis, but for the love of god, please make NPCs, especially companions/love interests etc., have realistic personalities and motivations. Hire extra people just to work on NPCs if you have to, in addition to the artists, programmers etc.
I also think that moving away from the supernatural cosmic aspects and more toward more "earthy" interests would be an interesting change. Like, instead of having a game revolve around uncovering and confronting supernatural threats to the fabric of reality, have the game focus more on mortal politics and such. Daggerfall did a good job with this I think.
For example, I'd love TES 6 to deal with the conflict between the Tamrielic Empire and the Aldmeri Dominion (Thalmor in particular). Don't have a god/Daedra be the true enemy or anything, but just really conniving and self-righteous mortals. Every other fantasy game out there has you fighting against crazy unknown supernatural whatevers. I think it would be a really interesting to just truly be fighting against mortals, without having the gods or other powers be pulling the strings. Sure they can have a presence, but I'm just starting to get tired of games where the mortals are always just pawns for the gods.
I actually thought Morrowind did this the best, since really, it wasn't any actual "gods" who were involved at all. Just mortals who had achieved a semi-godlike state but who were still very, very fallible.
For example, in Skyrim I was actually more intrigued by the Civil War and the conflict between the mortal factions, and less interested in the dragons and such. A move toward "low fantasy" as they call it (a la George R.R. Martin or R. Scott Bakker) would be welcome indeed in my book.