Predictions for Khans mechanics, some more likely than others:
Abzan (WBG) - "Whenever CARDNAME attacks or blocks, you gain 1 life."
Abzan does not appear to be graveyard focused, and the other major thing these colors share is life gain. At Comic-Con, Abzan was described as playing the long game, and constant life-gaining is a good way to extend the game. Lifelink is too strong to just put on every creature, so this seems like a good variation. It's kind of boring, but that's what Wizards often does. Abzan might also have a lot of "whenever you gain life" cards.
Jeskai (URW) - Spellmorph, because shut up. It could be like, "You may cast this face down as a 2/2 creature for (3). If you pay its spellmorph cost, or when it is turned face up, exile it and and cast it from exile without paying its mana cost if able."
Sultai (BGU) - Delve (each card you exile from your graveyard while casting this spell pays for 1), because Sultai has a mechanic based on resource manipulation and Wizards has been trying to fit delve into a set for a while.
Mardu (RWB) - Hard to say, since almost any combat mechanic could work. I'll go with fixed flanking, like, "Whenever a creature blocks this creature, the blocking creature gets -1/-1 until end of turn." Flanking mainly appeared in these colors, anyway.
Temur (GUR) - Like how Odric had a mechanic similar to battalion in M13, I get the feeling that Might Makes Right is a preview for Temur's mechanic. It will be an ability word with effects like, "If you control each creature on the battlefield with the greatest power or with the greatest toughness, then..." with the toughness part added for blue.