Feather:- I need to be able to carry more but i don't want to level up stamina as i want health and magika
You could make enchanted items that carry the same effect or use alchemy.
Levitate:- I loved this spell and i could now chase dragons in the air and fly up mountains this would be cool.
Will never happen it made dungeon and level design difficult. They removed it from oblivion because it limited the kind of things they could have in the game.
Open lock:- Yes the lock pick system has been improved however its nice to be a pure mage and to use magic as an alteranative.
The problem was a single spell made an entire skill pointless. Maybe they figured out how to make magic proof locks.
Slowfall:- Big high cliffs are a pain especially in the dark. Slowfall would help greatly falling great heights with no damage.
This would be nice
Waterwalking:- Not essential but i just liked this spell it was fun.
Also would be nice.
Nighteye:- Being able to see in the dark with out giving away your position would be handy as a thief and assassin. I don't like it limited to one race.
I think as a spell its gone forever, it actually makes the racial ability useful.
Mark and recall:- I know fast travel in some way makes this spell redundant however i used to use it to over burden myself and then teleport to my house to store items for sale later. Very handy and saved time. I was hoping it would be improved to add additional marks however it was removed from oblivion and has never returned.
That was removed for similar reasons as Levitation. It limits the designing of spacing and scenarios. Mark & Recall has the potential to break quests if you use it at the wrong time. I can think of a few quests or dungeons that could be potentially broken because you recalled out at the wrong place. What you really want is the long haul perk from NV that lets you fast travel when overencumbered.
If they did add it in, it probably wouldn't work if you were overencumbered kinda like the carrages or function in combat.