First, I was thinking about how Blizzard revamped paladin judgements in WoTLK, it was be nice if curses got a revamp to make them more interesting. Imo, rename curse of agony to just "agony" and make it a regular spell. Curses should be about utility, not damage, otherwise it's hard for utility to compete.
Now put curses on a collective say 45 second cooldown and make them strong enough to warrant a warlock wanting to use a curse for utility.
Curse of exhaustion immobilizes a target for 5 seconds.
Curse of weakness lowers a target's damage done by 25% for 10 seconds (PvE bosses immune)
Curse of tongues silences a target for 3 seconds
After siphon life and immolate were removed from affliction, It's kind of felt to me like affliction has lost it's "load em up with dots" feeling. I'm not saying affliction doesn't do great damage, corruption and UA do enough damage to make up for the loss of the 2 other dots. Just having two dots up just "feels" a lot different from having five up on a target to me.
I know Blizz doesn't want to make PvE affliction too complicated so I was thinking why not reintrodice siphon life as a utility spell that doesn't do much damage but provides good healing.
Other things I'd like to see:
A demonology specific spell so that it doesn't have to borrow its entire rotation from the other 2 trees. Maybe like a channeled spell that increases the pet's damage done for as long as its channeled.
Affliction talents reworked to make drain life the filler spell instead of shadowbolt. Kind of like how Blizz worked death strike into blood's rotation.
Drain soul made more practical. Since drain soul is how we get our soulshards now, warlocks are more willing to excuse this being a really clunky unheard of 15 second channel. Now that soulshards is no longer it's main purpose, it really needs to be improved. I don't reallly like the whole channeling a 15 seconds spell while also managing dots playstyle. Just make it a 1.5 second cast mind blast style spell that only does good damage if the target is at sub 25% health.
I'd also like to see more distinction between shadow priests and warlocks. They basically have their own version of UA and death coil now. Once siphon life was removed and immolate made exclusive with UA, affliction uses the same number as dots as shadow. I think warlock's made their distinction originally for being heavily drain oriented.