Other spoilers:
This was leaked before, and everyone agrees that it will see a lot of play, including in Modern Tron decks.
Lands, which were specifically named such that they can be reprinted in any set:
I'm assuming they made these instead of using the Khans dual lands because they don't always want to create a grindy environment where everyone is gaining incremental life.
Articles:
Making Magic - A Solemn Oath, Part 2 - Some interesting stuff in this article:
* They decided to make surge a cost reduction mechanic instead of an effect booster so that you could use it more easily in one-on-one.
* Support originally not just added +1/+1 counters to creatures, but also loyalty counters to planeswalkers. The removal of that last part was a very late change, due to them being worried on its effect on Constructed.
* In the past, they were against small/small/large drafts because they didn't think it would work out, but with all the other shake-ups, they decided now was the right time to investigate this under the assumption that it could work, and they came up with the solutions covered before (more cards, less cycles at common, etc.).
* Surge and support were made in design, but design's new Ally mechanic triggered off of an Ally dealing combat damage. Development decided that the gameplay was too similar to what Ally decks already do, and came up with the cohort mechanic based on the Onslaught cards where you tap two of a creature type for an effect.
* They realized that the above wording caused a lot of confusion over whether you could tap the creature on the turn it came out (you can), so they changed it to the current wording, where it's a tap ability, and thus is affected by summoning sickness.
* MaRo came up with the "Oath of ___" cards based off of the Justice League. They were specifically designed so that they could print a new one with the same format whenever a character joined the Gatewatch. MaRo's wording definitely implies that they are expecting other characters to join the team. Also confirmed that Ob Nixilis is not getting an Oath in this set.
Reconstructed - Kozilek's Return - Goes over the card in question.
You Can't Always Go Hame - Goes over the uncommon dual lands.