Pet Scaling. Warlock pets do not scale well at level 70 and as a result, lack sufficient stamina, mana, damage, and resistances.
Spell Haste and DoTS. Spell Haste should have a positive effect on DoTS, making them tick faster without gimping their dmg output.
Spell Pushback. With the advantage melee has been seeing over cloth wearing classes, and the introduction of Ignore Armor, the spell push back mechanic needs some tweaking to favor successful casting.
Talentless Insta-cast Corruption. Given the limitations placed on the spell's dmg coefficient, how easily the DoT is removed, and that global cooldowns already act as a limiting "cast" buffer, making it available to all Warlocks as an instant-cast "on the run" spell isn't too much to ask.
A True Unstable Affliction. It's a 41-pt talent. It's negative effects should proc every time the DoT is removed, no matter the process used.
Consolidate curse buffs into one Malediction. Since we can only have one curse on a target at a time, we shouldn't have 3 separate talents improving our curses.
Contagion vs. Unstable Affliction. These two talents seem to compete with one another. What makes UA great is it's negative proc upon being dispelled, but Contagion, the talent that leads to it, reduces the chance it will be dispelled. An obvious logistical error that needs a fix.
Improved Shadow Bolt and Incinerate. As things are currently, Fire 'locks do more damage spamming Shadow Bolts than they do spamming Incinerates. The Improved Shadow Bolt talent should also apply to Incinerate to help fix that inconsistency.
Affliction Tree Crit to Dmg Conversion Talent. DoTS are totally gimped when it comes to stats, and the updated effect of Resilience makes them even more so. To help balance out the new, almost universal defense players have to DoTS (everyone has access to 300+ Resil now) and to help Affliction's viability in high-end raiding (where gear is more Crit and Haste-heavy), introduce a talent deep into the Affliction tree that converts a percentage of +crit to +spell dmg.
Soul Shard Mechanics. Soul Shards have such potential, but currently are very basic and almost completely unnecessary. If they are to remain as generally applicable as they are, either introduce an ability to conjure them at the cost of the Warlock's own health (maybe make that the effect of Imp Drain Soul), or make them purchasable reagents. However, I think it'd be better to introduce mob-specific Soul Shards that when drained and created, add special effects to the Warlock's abilities that require shards. For example, creating a Soul Shard from a fire-based mob could add spell damage to a Soul Fire, and when cast, the Soul Fire would give priority to the fire-based Soul Shard for consumption. Similar mechanics could be applied to Shadowburn as well. And how about boss-specific Soul Shards that are made to be useful during other boss encounters? For example, a spell cast using a shard gathered from Onyxia could be programmed to be incredibly effective against Nef.
Cataclysm and Aftermath. Replace with more useful, Warlock-centric talents, or improve them by increasing their proc or return rates. Perhaps introduce a Suppression-type talent for Destruction spells, or one that increases spell crit rating.
Demon Armor. Allow it's health regen to scale, and increase the armor it provides. Adding Resilience to it wouldn't be a bad idea either.
Curse of Weakness. Buff it, and allow it to stack with other AP reducing abilities.
Utility Curse Mechanics. Allow them to be stacked atop one another, but with diminishing effects. For example, 3 Warlocks cast Curse of Shadow on a single mob -- the first increases Shadow dmg by 10%, the second by 5%, and the third by 2%, etc.
Demonology Talents. There are far too many weak talents in the Demonology tree. Master Conjurer, Imp Enslave Demon, Imp Health Funnel, and even Imp Succubus and Voidwalker all need to be reworked or replaced altogether.
Firestone. Revamp to add a stackable scorch effect to fire spells instead of melee procs. That way, it'll actually be an attractive prospect for Fire 'locks.
Conflagrate. Needs to be reworked to scale better with the 'lock and his/her gear.
Amplify Curse. Make applicable to ALL curses, as well as making the casted curse immune to all dispelling effects.
Shadowfury. Make it instant cast, as was originally intended. It's a 41-pt talent, and should be worthy of that title.
Drain Soul. Rework to make using ranks other than Rank 1 worthwhile. Increase dmg or make it tick more often, or include a paralyzing or slowing effect similar to Mind Flay.
Here's hoping for a Warlock Christmas!