Mine are:
1: A visibility gem a-la Thief series
(a good idea on how to incorporate this into how skilled somebody is at stealth is: If somebody is a novice at stealth, the stealth gem may not appear but once for example the shadow creeper is an apprentice, the gem can only get to a certain level of darkness... but once the thief/assassin is a master at stealth, the visibility gem can become fully dark once the character is in a shadow) hope this makes sense.
2: Some randomized dungeons with associated randomized quests just like Daggerfall had, I feel that this feature would GREATLY add replay value to the game.
(One of the few things I feel I would've liked better in Oblivion is that I was limited to the amount of dungeons that were built into the game and not to mention quests... The modding community did a great job at adding new content but I didn't always enjoy having to search for new dungeons online to plunder before I had the chance to do so)
3: Difficult to achieve guild perks such as: Spellmaking, Unique talents/spells, item enchanting, houses, etc etc etc..
(This will allow a person to thrive for something and add another level of "achievement" to the game which many people crave)
4: A hardcoe mode a-la New Vegas I enjoyed how I had to actually "survive" in the game and not only fight monsters
5: An integration of Mass Effect style interaction with important characters, Daggerfall style interaction with generic NPCs and a Fable 2 style reputation system.
(I feel that one of the most important parts of playing a role in an RPG is getting in-game feedback on your character. This will make the many NPCs give actual LIFE to the game rather than feeling like most are there just imaginary people)
Well, there's my wishlist