Without further ado I will get to it:)
1.God worship
There are a lot of gods in the Elder Scrolls, and everyone has some sort of alignment or preference to some god or gods, be it Daedra, Aedra, or some other deity that I yet don't know about. I think it would be cool to have some sort of mechanic that will upon the worship of some sort of deity or deities add bonuses to your character, the more gods you worship the less effective bonuses are but you have more of them on the other hand. If you worship one god the effect is the strongest. Also there would be different types of rituals for each god, three to be precise, for mage, warrior and thief. Add some quests to those gods also. I just play a Dunmer and after Morrowind game(not expansion) I really dislike the Tribunal, not to say that I liked them from the start though:) But the other religion that Dunmer have is a Daedra worship, and I would like my elf to be a part of that. I think many players would like to have one more edit mechanic that will make his or her character more unique.
2.Spell/Ability edit
While I would like to see new trees and new abilities but I think ZOS doesn't consider that kind of threads from players. So..... What I am suggesting is to make some kind of ability crafting mechanic where you can edit it purely cosmetic or change what kind of damage it does(this is not for everything). For example sorc overload can be morphed into fire ability instead of storm etc.
My intentions with this thread is for ZOS to add more editing options to your character. In my opinion the more you can make your character more unique the more enjoyable the game will be, and I think this is what Elder Scrolls games are all about, "play as you like, be who you like" I want more fire stuff, but I am limited by my class, this is not the Elder Scrolls way in my opinion.
So ZOS.... Even if you won't make changes that I described, and I am very skeptical that you will, but at least add more options to our characters.