Blizzard gave us a handy overview of the new 1-5 player 10-15 minute Delve mini-dungeon feature! From their role-independent nature to their tier difficulty levels, the companion NPC and his specialization and curios, the 12 unique Delves (and the special single-boss 13th one), Delve variants, rewards (going up to Heroic raid level/M+5 keys), the customizable mount, and more. 

Here's a preview of Arathi Lynx mounts coming in The War Within expansion.
The mounts currently have no source indicated and come in various tints as shown below.
Black

Brown

Gold

Red

White

Let's take a better look at Delves, one of the main features of the upcoming expansion.
Delves Entrance & Start
When you enter a Delve, you will see a UI with more details about your run, including a dropdown for difficulty and the items you'll get upon completing the delve. Entering a delve is seamless and there are no loading screens.

Hovering over the icons will provide you with information about the delve you're about to complete.

Delves Companion
The companion for Delves in Season 1 is Brann Bronzebeard. You can adjust his role in the new hub or at the beginning of a delve. As you complete more delves, Brann gains Experience and levels up, gaining access to new abilities.

Delves Run
You can play delves alone or with friends. One run will take up about 10-15 minutes. Every run consists of multiple scenario steps / objectives you must complete to get to the end and claim loot. This can be as simple as helping unwrap stuck miners to escorting your party to safety.


You can also unlock respawn points where you'll end up when you die.

You can open treasure chests for Torghast-like anima powers, kill Elites for XP or even complete quests inside Delves.

Delves will end with a Rare Elite just like Torghast.

When the elite dies, you will enter a treasure room with multiple chests, but you can only open one because other chests require rare and epic keys, which you must buy from the quartermaster.
 
Rewards from Delves
The Delves quartermaster is a none other than Sir Finley Mrgglton who sells various head/back cosmetics for Resonant Crystals.

The following items are currently available on the Alpha:


One of the selling points of Delves is a fully customizable plane mount called Delver's Dirigible, but we're not sure how to get it yet, since the item's not on the quartermaster.

 

Warlocks will be getting quite a few changes in upcoming Alpha builds as well, as Blizzard give us an overview of talent changes.
Warlock (Source)
Greetings Warlocks,
We’ve been very excited to see the community’s reactions to the Warlock Hero Talents, and we appreciate all of your feedback.
In the coming weeks, you’ll see multiple changes to the Warlock class and specialization trees, and we’d like to provide some context for these changes here.
Core Goals
Ensure each capstone is interesting and exciting. Reduce the amount of throughput talents, to free up utility choices. Reduce the number of ranks for talents that don’t warrant multiple ranks. Affliction
The Affliction specialization tree forces a choice between a single-target or multi-target profile rather than providing a viable build that is adaptable in both situations. We want to redesign, introduce, and remove talents, as well as address the tuning of Malefic Rapture to help reduce this friction.
Demonology
For Demonology, we want to address the number of long cooldowns available as well as reduce the amount of resource flooding. We’ll also look at underused talents such as Doom. The feedback provided during Season 3 was instrumental in helping illuminate a path forward for Doom, and you should expect a redesign of it in a future build.
Destruction
For Destruction, we have plans to reduce the fluctuation in power based on target count. We also want to take another look at how Destruction plays in multi-target situations and look for ways to improve underused talents such as Cataclysm and Soulfire.
More to come
As always, we’re reading feedback and discussing other changes. We’re still monitoring discussions about Hero Talents, and will make adjustments as needed.
Thank you for your thoughts thus far. We look forward to hearing more as development progresses!

We have yet another interesting set of mounts coming with the next expansion, and while they're not... traditionally pretty, they sure are cool! The cave grubs are another ground mount in an expansion that is really focusing on flying, with the Dynamic Flight expansion of Dragonriding, so we really hope that rumored dynamic ground mount system comes in sooner rather than later. Could this be another burrowing mount perhaps?
More cool looking Mounts from The War Within Expansion in #worldofwarcraft

This one looks Nerubian inspiried, which is very cool! pic.twitter.com/SZRY6rdg2Y
And here's the mount special animation, courtesy of keyboardturn: