Things I would love to see aded from an assassins point of view would be throwing knives which take the backstab bonus, and garrottes for guaranteed silent kills on light or non armored mobs( not that that's particularly accurate either).
likewise, the ability to knock people out should alse be dependant on the armor they are wearing. Are you really going to puch someone over the head when thay're wearing a full helm ? Perhaps have a billy club or something. If you want somethign immersive you have a variety of moves dependant on the opponent which you can pick up as stealth perks. so lets say at 30 stealth there's a perk to knock unarmed folk out. At 50 sneak a perk to use a billy club to knock someone out wearing light armor, at 70 sneak you get a perk to use skyrims equivalent of chloroform or something on plated folk.
The one biggest thing though that I could use as a sneaky type early in the game, especially when playing with increased spawns is some distraction method other than attempting to shoot an arrow beyond sometwhere which never seems to work very well for me. .. I know there's throw voice shout, but I was thinking there shoudl be someway of diverting enemy attention to allow a quick sneaky dash behind them.
Anyway .. thats my tuppence worth, hope its helpful.