Hey!
I wanna write about what I'd buff for each build (PVE/raiding perspective). List-like, wanna keep it short. I don't wanna make any build good at everything, weak spots have to exist. Will mention things which I think would make them more fun for PVE.
Prot warrior
* + rage when being hit talent at the bottom of the tree
* buffing shield abilities (more threat, maybe less rage cost/CD)
Fury warrior
* maybe some itemization during leveling/early raids
Arms warrior
* a raid utility debuff
* maybe + weapon skill for those weapon mastery talents
Prot pala
* better ardent defender
* maybe a range pull
Ret pala
* better dps/threat ratio
Holy pala
* some variety at healing; a sometimes used secondary healing spell would do
Ele shaman
* threat reduction
(* mana is kinda handled with custom items and consumables)
Enh shaman
* increased damage
* more talent interaction between melee and spell crits/hits (can't properly equip themselves for both) - also, better organized talent tree so they can take every talent they need for the build
Resto shaman
* better deep-end totem talents (restorative totems + mana tide)
Bear druid
* added threat to swipe
Cat druid
* cleave
Moonkin
* moonkin form containing mana regen (like 10% of your normal mana regen continues while casting)
Tree
* allowing hot stack to a limited degree (like 2)
* out of combat rez
Rogue
(Combat, both for swords and daggers)
* retaining at least some energy when switching targets (general change)
* 'nature curse' poison for rogue raid utility
Fire mage
* spell penetration talent
Arcane mage
* a leech talent -> dealing damage recharging arcane mage's mana. would work well with the mana regen utility build
Frost mage
* a raid utility which doesn't effect PVP anyhow. not sure, what. idea is to have a reason to bring 1 frost mage even to Naxx if possible
Warlock general change: draining an elite gives 2 soul shards not 1. big qol change
DS/Ruin warlock
* better sacrifice reward for doggo. succubus + life tap already takes care of the mana regen
MS/Ruin warlock
* amplify curse (slightly) affecting cor, coe and cos
Holy priest
* more interesting holy champion rewards
Disc priest
* a deep-end talent making shielding viable without breaking pvp
Shadow priest
* small CD spell cleave. can't be spammed.
Hunter general change: further increasing pet avoidance (reduced damage taken from aoe/cleave)
Survival hunter
* in-combat traps
* better raptor strike
Marksmanship hunter
* improved arcane shot giving +damage based on agi to keep it relevant
BM hunter
* an ability increasing pet damage+haste while making you unable to shoot/attack in the meantime. for the true pokémon roleplayers