We're taking a closer look at Worldsoul Memory, a new open-world event that will be part of the War Within pre-patch, and later, Khaz Algar.
In the War Within pre-patch, the Worldsoul Memory event will take place in 3 different locations across Azeroth. Basically it's the same version as we'll see later in Khaz Algar.
Places with Worldsoul Memories will be marked on your map, here's one in the southern Isle of Dorn.

Before you can start the event, you must farm Radiant Echoes from mobs in the open world by combining 10 Radiant Chords.
When you enter the area with a Worldsoul Memory, there will be this giant Azerite ball that you must interact with to begin the event.

Subsequently, a new window will open, informing you about the event. As said above, you must deposit 1 Radiant Echo to receive the Worldsoul Memory buff for 5 minutes.

While under the effect of Worldsoul Memory, you will enter a different phase, where you must kill mobs and elites under 5 minutes.

These drop Coffer Key Shards that are combined into keys used in the treasure room to open Bountiful Coffers when you complete delves.

When you complete your first Worldsoul Memory event, you will receive The First Echo and unlock even more difficulties.

The next time you will start the event, there will be more options for you to choose from, you can:
Spend 1 Radiant Echo again to start a Radiant Echo; Release 10 Radiant Echoes at once, increasing your rewards from this memory tenfold; Start a Radiant Discord, which is the hardest difficulty for this event and the Mythic Challenge means you will lose the  Worldsoul Memory upon death and be immediately removed from the vision, meaning you must again spend echoes to start anew.
There are multiple Worldsoul Memory Events available in Khaz Algar and all have long timers, so if you're looking for that endless grind, you will only need a lot of Radiant Echoes.
Rewards
Fragments of Memories rewards the Memory Chord toy. Echoes of Danger gives you the Echochaser title.

We have confirmation that the only way to get the World Boss mounts in Mists of Pandaria Remix is via Bronze! 
World Bosses (Source)
Telinastus: In Remix, yes. But don’t forget that you can go pummel those same bosses on your Dragonflight characters.
A basic rule-of-thumb for Remix is: quests drop their original loot, but bosses do not.

We have an almost quad-feature in the hotfixes today, as retail, Remix and Cataclysm Classic have quite a few improvements, and even Season of Discovery sneaks in with one! From trinket changes in 10.2.7 to cloak achievement and Yak Fur fixes in Remix, class adjustments and double BG honor in Cata, there's plenty to see.
 June 3 (Source)
Dungeons and Raids
Neltharus Fixed an issue where canceling Dragon Strike using invisibility will lead to Chargath not casting Grounding Chain. Items
Fixed an issue where Augury of the Primal Flame would not proc certain effects such as Seal of Diurna's Chosen and Seal of Filial Duty. Fixed an issue where Tome of Unstable Power could proc from non-class spell effects such as self-damage from Vessel of Searing Shadow. Player versus Player
Victories in Solo Shuffle now reward 5 crests (was 3) and victories in Rated 2v2 and Rated 3v3 Arenas now reward 2 crests (was 1). WoW Remix: Mists of Pandaria
Mini Mana Bomb (Horde) and Theramore Tabard (Alliance) are now available from Horos at any Infinite Bazaar for players who have completed Theramore's Fall for their given faction on any Timerunner. Developers’ notes: There is no more need to complete it at exactly level 35. Fixed an issue where some steps of the Infinite Power achievements could be skipped for players. Tuft of Yak Fur, am I right? Now they stack. Cataclysm Classic
Honor rewards from completing a random battleground or a holiday battleground have been increased by 100%. Fixed an issue with Admiral Ripsnarl's visual effect. Fixed a bug preventing the completion of the achievement Acrocalypse Now. Priest Atonement healing will now de-prioritize pets, and will only heal them if their health is very low compared to available player targets. It will treat them as if their health percentage is 50% higher when evaluating targets. Fixed an issue with Shadowy Apparitions that prevented them from being summoned under certain circumstances. Shaman Fixed a problem with Precision where it was granting an unintended additional 1/2/3% chance to hit. Season of Discovery
Addressed an issue that caused quest "Goblin Solutions" to sneakily steal extra mines from you.

Blizzard have announced new dungeon tuning coming with this week. Neltharus and Uldaman are getting some changes starting with the weekly reset. 
Tuning (Source)
With hotfixes that will go live during scheduled weekly maintenance this week (tomorrow, June 4 in this region), we will make the following tuning adjustments to Neltharus and Uldaman: Legacy of Tyr dungeons.
Dungeons
Neltharus Chargath Slag Eruption duration reduced to 3 seconds (was 4 seconds). Fetter duration increased to 15 seconds (was 12 seconds). Addressed an issue where canceling Dragon Strike using invisibility will lead to Grounding Chain not being cast. Uldaman: Legacy of Tyr Bromach Quaking totem’s health reduced by 10%. Emberon Addressed an issue where Purging Flames’ visual does not line up with the beam area.

Here comes a brand new War Within trailer, featuring Xal'atath, Alleria, Anduin, and more! We get a classic villain monologue, as she dives into our heroes' perceived faults, and we even get a look at Magni and a pissed off Thrall!
The War Within Beta launches this week, on June 5th, so make sure you've opted in!