Anything you thought up, or maybe even stuff that was once canon but is no longer. What do you wish was part of the lore as it is?
For example, I’d like to see druids able to perform chameleon like manouvers in lore, able to swap colors in nature to keep themselves stealthed.
Warlock Licences. It is peak Guard RP.
I mean. That’d be just people saying they got one maybe.
That your parents actually loved you.
Can you get a Doctorate in Warlock?
Tensions between the Trade Princes whose ripples could affect the course of Azeroth’s history.
Also wish that goblins on Azeroth had figured out how to build a train network by now.
I also wish that Ratchet had a gambling district with expensive food shacks that bleed a gambler’s pouch dry.
That Azeroth isn’t a titan.
Silvermoon City is rebuilt but the illusion of a destroyed City is being kept up just for the sake of it.
Any of the little details about specific races or cultures coming from this thread. Ideas like this flesh out the world and make it so much more immersive.
Goblin cities like Ratchet, Gadgetzan and Bilgewater Harbour being actual cities and not just looking like small port towns. Trade fleets and constant trade wars between various Cartels. Give me ALL OF IT!
Pandaren were a mistake and never existed
A post I sadly can’t find anymore, but it’s a headcanon I really like that is simply too large to sneak into RP without it actually being canon.
The headcanon is that pandaren have a caste system where the red-furred and grey-furred ones are separate, featuring cultural as well as some minor biological differences.
Grey ones are stronger, tougher and have more endurance, and are more numerous, the lower of the two castes. They are builders and farmers as well as soldiers. Then the reds, who are quicker of body and mind, serve as leaders, scouts, messengers, riders and so on.
The twist would be that, since they are still pandaren, it would be a harmonious relationship. The lower caste wouldn’t really be oppressed, unlike the caste systems in real history. You could introduce aspects like monkhood wherein the caste systems are discarded and interesting plotlines where the caste lines are crossed - being considered oddities rather than crimes.
Means Streets of Gadgetzan version of WoW Gadgetzan when?
that warriors use a rage-powered magic instead of being supposedly magicless while having obvious magical shenanigans going on with their strength and leaps
I really like this one! And there are hints of it being possible in WoW too. While there are exceptions to this of course, most of the grey-skinned ones we’ve seen have been exactly what you describe, farmers, physical labour and/or warriors, where as the red ones, particuarly the females with the longer tails, have been portrayed as rogues/mages etc and more agile work. Again, not universal, but there is enough of it to make this headcanon actually believable and plausible 
A lot of stuff from the RPG sounds pretty cool.
That Kil’jaiden was infact behind the veil of spirits telling Vol’jin to name Sylvanas Warchief, just like he prank called Ner’zhul.
The most recent Legion invasion was a feint to lure us into a false sense of security by making us believe they were out for good, when actually the real invasion is coming and now we’re even more off-guard than we usually are.
Sargeras is all good. He left his sword behind as a gate.
Wrathion was right all along.
Another idea of mine was a sword that was cursed to be able to completely feast on any spell and resist it, basically drinking its mana, but at the cost of constantly draining the mana of the user and when that’s gone, their life force.
That the scale of the world is only adjusted to the game, and that there are in truth numerous villages and towns hidden all across the world. Would make the “why is Gadgetzan and Ratchet so smoll” more believable. So imagine that on the road between Goldshire and Stormwind there would be like two, small villages, of ten houses lets say, called (an example) Greendell and Bywater. Actually hope blizzard releases something akin to chronicles but with atlases!