While we still don't have any official word on what the upcoming block to begin with the Fall 2014 large set is, there is some pretty strong evidence that it will be Central Asian-themed, with a combat mechanical theme, and called either Warlords of Khanar or Khans of Tarkir. Either way, it takes place on a world we've never seen before, but given the real world history and culture that it's based on, we can make some decent educated guesses about its flavor and mechanics.
- A play-lots-of-creatures theme. After all, the Mongol Horde wouldn't be a horde if it didn't have lots of members. Rather than the "make one thing big" battlecruiser Magic ideas that underpinned sets like Rise of the Eldrazi and Theros, the upcoming block could emphasize building an army out of component parts that can be used for varied strategies and especially work well together.
- Lords of the sky. The supreme deity that Temujin, aka Genghis Khan, worshiped was Tengri, which means "the Eternal Sky." And no wonder he was a sky god - the heavens were the biggest continuous thing the steppe people could see. Perhaps Khanar has a race of Aven, or bird-people, who are named something like the Tengri.
- Horses and archery. Mounted bow-wielding is kind of a big deal in Mongol culture, and it was the favorite combat style of the Mongols throughout the period of their continent-wide empire. Expect a lot of Horse and Archer creatures - and possibly R&D's first real attempt at the infamous "mount" keyword that just about every custom Magic card designer makes.
Got any other ideas of what you want to see from the upcoming block? Let me know in the comments.