The things I would love Bethesda to try to incorporate into Skyrim or any future sequels focus mainly on your character's helper/horse.
1.) I would love to have two simultaneous helpers, making it sort of like a gang. Imagine having one helper a mage, another a barbarian, and you a thief or all three of you the same classs, any combination, eh?
2.) Let's take it a bit futher. Customizing your helper/helpers! It would be nice to give them perks to focus on, but if I'm asking too much, being able to name them, change their facial features, clothing, and weapons will be good enough. ( I understand you can somewhat control what your helper wears/uses as weapon, but it is very limited.)
3.) It seems kinda mean to ride around on a steed when your helper has to hoof it by themselves. I know the game usually makes them disappear and reappear when you have stopped along your journey, but why not be able to purchase a horse for them. And when they don't own one of their own let them ride with you on your horse. If falling off cliffs or some other stupid thing that could easliy kill your helper while on their horse is the problem then why not make them immune to damage taken from falling off mountains?
4.) I would love to be able to chop a dude's head off while I'm on horseback! Shoot some arrows or throw some fireballs while on your horse. Can you imagine fighting a dragon ( or your whole gang ) while doing circles around it on your horse delievering punishment if you have the skill? It could be incorporated as a perk even.
Well, that is my two cents for now.
1. Someone will mod this into the game. Similar limitations existed in Morrowind, Oblivion, Fallout 3, and Fallout: New Vegas, but it doesn't stop me from having a small army at my back now.
2. Custom inventories were modded into previous games as well. Now, renaming and changing the facial appearance would be very complicated, and could mess up the game. Custom stats... Ehh, it's tough to tell. I'm sure it could be done, but I'm not sure of the possibility of changing their leveling patterns.
3. More importantly, why aren't there any NPCs on horseback at all (at least as far as I've seen)? Especially couriers; it'd make sense for the guys who travel all across Skyrim to be mounted. And why no mounted patrols?
4. I believe horse combat was omitted intentionally, as it'd be way too powerful. That being said, it was modded in to Oblivion, albeit imperfectly. Were it to be put in, there would have to be some disadvantages beyond the lack of agility. For example, a power attack should have a chance to knock you off your horse, as should any attack that can knock you down in regular combat. And if it is put in, I'd like to see it incorporate #3 and let NPCs fight from horseback as well. Imagine setting up a large battle, and seeing a large cavalry charge.
Conclusion: Wait for mods. They'll fix anything and everything that may or may not be wrong with this game.