So I've played all TES games so far, and have a few ideas that I'd like to see:
Dynamic Quests: In Skyrim, the Dark Brotherhood missions were lacking in skill. What I mean is, that in Oblivion there were mini objectives in the assassinations such as: Locked in a mansion with 7 guests and you had to kill them all without any of them figuring out you were killing them. I would like to see these sort of side missions in the Dark Brotherhood or other organizations.
Buildable Locations: Sort of like Hearthfire, however more like Fallout 4. You can put an outpost or a town or a castle/hold somewhere. Villagers or Refugees come there to seek a home, and they can be given different tasks such as gathering food/herbs/ore etc. Each person requires a bed, however you as the main player can set your own personal house/room. I enjoyed the Fallout 4 builder, however in the new TES game, it would be more enjoyable to have more interactive decorations (shrines that play a song(s), a mirror/portal you can build to contact other settlements) as well as when you build a structure a certain way, it will unlock something new (such as: if you build seats in a certain arrangement facing a staged area, you will unlock entertainers/actors to your settlement that will perform shows or tell tales a couple times a week). As well: waaaay more stuff to unlock in the game world. In Fallout 4, there were 4-5 magazines that unlocked about 20 different things. This was very disappointing when I found them all because I thought there would be more.
Fast Travel to Specific Points Only: So, instead of every significant place having a fast travel point, only have one every so often so that there will be more exploration. As well as having a very big choice of mounts: Horses/Lions/Lizards/Boars/Wolves, etc.
Flying Mounts?: Some places in the game will be unreachable unless you have completed a portion of the game that unlocks flying mounts OR dwemer airships.
Races: Please have some of the mentioned in the past TES games (snow elves, dwemer, daedra) that you can play as.
These are some of the things I would like to see, but no matter what I'll probably still play the next TES game.