Some of these are already being discussed in other forums. TH is being discussed in the forum above this one which has also branched off into discussing several THF abilities especially steal & mug.

Job Ability: Snatch
Level 10
Recast: 1min (or less)
This version of steal allows thieves to acquire "temporary items" from monsters, like potions or grenades.
I just posted a similar suggestion in the forum above this lol. Though I think being able to steal an unlimited amount of temp items & every minuet might unbalance things, especially if they're powerful items.

Job Ability:Borrowed Time
In the past, this has added Stop to the target. In FFXI, this could add slow to the enemy, and haste to the thief.
Despoil already has a chance -crappy though it is-to add slow depending on mob. A haste ability would be nice though.

Job Ability:Stolen Heart
....This could simply be a way to stop a battle and get away. The enemy may give the Thief a gift.
THF already has flee & hide to escape battles though admittedly these aren't always 100% effective. I'd like to see a beastman after trying to rape my ass stop & give me a brightly wrapped present just for lolz or a mandy give me a flower just for cutez. Though would you want some of the things monsters would try & give you? I mean my cat brings me 'presents' all the time I'd rather not receive.

Job Ability:Pilfer HP
I actually posted a similar idea to this as part of my post on the dual wield forum (sounds like a strange place to post it I know but the discussion there has also branched off into various THF related issues). I think having a way for THF to recover some HP besides bolts which aren't as effective as they used to be would be great.

Job Ability: Entice (or Lure)...
...The purpose of this ability is to allow Thieves (or people who sub thief) to pull monsters that would ordinarily link.
Would be handy but I think if SE wanted people to be able to pull easily without linking they wouldn't have made mobs link to begin with

Job Ability: Distract
Level 40
Duration: 30sec
Recast: 2min
Removes position restrictions on all actions taken against the distracted target. (Sneak attack, Overwhelm, Closed Position, etc)
This I really like, being able to use SA solo other than as an initial attack or with hide would be awesome. Would also be great for avoiding SA misses when someone turns the mob right before you WS.. because someone always does..

I would ATLEAST like to see SE alter the range for TA, do you have any idea how hard it can be to TA a moving taru especially if they're surrounded by other players or mobs SE? Well do you?!