Today was the big moment. As promised, Mark Rosewater announced the upcoming fall large set in a video alongside Rich Hagon on the last day of Pro Tour Journey into Nyx - and as expected, it is the Mongolian-themed Khans of Tarkir. The MTGSalvation.com Rumor Mill thread on the Khans announcement sums it all up pretty well:
The set is named Khans of Tarkir.
Its expansion code is KTK.
It was formerly known by its codename "Huey".
The other two sets are unknown, but the names Dragons of Tarkir and Warlords of Khanar have also been trademarked by Wizards of the Coast.
The set will release September 26th 2014.
Creative and Story
The plane of Tarkir is war-torn by warlords.
There used to be mighty dragons on Tarkir, but they have all been killed.
It is the home world of Sarkhan Vol.
He left his home world in order to encounter dragons on other planes.
The story takes place after the last time we saw Sarkhan.
Design and Development Teams
Mark Rosewater is the lead designer of the set.
Erik Lauer is the lead developer of the set.
Innistrad and Theros had the same lead designer and lead developer.
Design and Mechanics
Sarkhan will appear in the set.
It is a Large-Small-Large block.
They are doing something they have never done before with the block structure.
The block contains two things that players have been wanting for a long time.
One of them is something they are bringing back after a long absence.
The other is something they haven't done yet.
There will be substantial news on the set during San Diego Comic-Con on July 24-27.
Of note, of course, are the announcement pictures, for many reasons. The darkly majestic army portrayed in the main picture has two races making it up - humans, and one other species of gray-skinned huge fanged goliaths, including the most prominent person in the artwork, the warlord leader. Whether these are Ogres or Orcs or something altogether different is yet unknown.
It's also impossible to miss the undead Dragon backing that army up - and since that species has been hunted to extinction on Khanar, all of the ones that appear in this block will necessarily have to be undead.
The set symbol is shown as mythic rare orange crossed scimitars on the background of a red shield - possibly this indicates polychrome expansion symbols, for the first time in Magic's history!
Sarkhan looks to have regained his senses after Bolas drove him insane, and will probably be black-red-green in the version we see him in now.
As for the much-requested returning and new mechanics, could we possibly hope for morph and a sixth color? Well, there's always hope - but my skepticism about both of those is understandable.