Which plane will we revisit next?

Right up until Onslaught block ended, the action of Magic's story was confined to essentially one place: Dominaria. There were some side trips, granted, to Rath and one to Mercadia, but we were really following the Dominarian heroes aboard the Weatherlight, the planeswalker Urza and his friends, and their efforts to stop the Phyrexian menace. Then things changed with Mirrodin block: It became apparent that there would be a new setting every block. Time Spiral block sent us back to a post-apocalyptic Dominaria for some closure, but then it was back to a new place every year. But there are only so many locations in the Multiverse that we can be expected to keep track of, and Scars of Mirrodin revisited a post-Dominaria plane with a story that changed the very nature of the place. Two blocks later, after Innistrad made its debut, Return to Ravnica confirmed that the "back to a plane of the past" thing was not a fluke.

Since Scars of Mirrodin and Return to Ravnica both headed off very successful blocks, R&D is assuredly going to send us back to an old plane - as an educated guess, let's say it'll be a block after the upcoming "Friends" block. Now, Scars of Mirrodin and Return to Ravnica were both released exactly seven years after their respective original sets, but that's probably not an exact rule to determine when a revisit block will come out. So let's see if we can rank the planes of the past few years in order of the likelihood that we'll come back to them in 2014 (1 being next to impossible, and 6 being extremely likely):

1. Kamigawa. Let's be blunt - the Kamigawa block did not sell well. This is due to both poor, parasitic mechanical implementation (the Spirits and Arcane spells all depended on each other to the point where one had to build a deck containing nothing but Spirits and Arcanes, and weren't even very good when used together), and the Japanese-esque flavor of the setting being alienating to Western players. R&D took a gamble with this world, and though it did have some very cool flavor and a good story woven through it, it didn't pay off. It would be hard to convince the top brass at Hasbro that a second iteration of that world would bring in high sales numbers.
2. Lorwyn/Shadowmoor. This setting was done in by the same things that hurt Kamigawa. The two mini-blocks of two sets each comprising four total sets was a bold move, one that highlighted the contrasts between the "day" of Lorwyn and the "night" of Shadowmoor. Lorwyn, sadly, essentially required you to build a tribal deck, which turned off the kinds of players who didn't want to do that, and its faerie-tale atmosphere was dismissed as too twee. Shadowmoor fared rather better, since its colors-matter theme was much more open and interacted with other sets way more so, and its dark-Celtic-mythology elements were better regarded. Still, neither block was terribly well-received.
3. Innistrad. Everyone seemed to love the Gothic-themed world of Innistrad, at least for the first two sets, when monsters roamed and killed freely and humanity was backed into a corner. Then the divisive Avacyn Restored came around, threw out most of the mechanical themes of the block, and brought back a deus-ex-machina fleet of Angels to fix the world and usher in an unambiguous happy ending for perhaps everyone but Garruk. To put it bluntly - while it might be interesting to see the aftermath of Avacyn's triumph (perhaps she's let it all go to her head and instituted a repressive regime, repeating the themes of the original block but with white as the villain rather than the hero), there might not be much to do when we get back there.
4. Alara. The once-sundered Shards of Alara are now one plane again. And its citizens must deal with four groups of new, hostile neighbors as well as the continuing machinations of Nicol Bolas. Some of these themes were addressed in Alara Reborn, and we're just ending a multicolor-themed block this year, so we're pretty sure to come back here, just not in the near future.
5. Mirrodin. There are a lot of individuals with unfinished business on Mirrodin. When the Phyrexians finally won the war and terraformed the plane into New Phyrexia, every surviving planeswalker who aided the Mirran resistance teleported away, swearing vengeance on the oil-formed monstrosities. That's sure to be an exciting time when they finally do go back, but the only knock against it is that it's too soon to have a second revisit.
6. Zendikar. This is the one - I have a feeling we'll see more of the "plane of adventure" in a not-too-distant block. When last we left it, Gideon and Sorin had both fled - the former to Ravnica to train with the Boros Legion, and the latter to Innistrad to repay old debts and reconcile himself to his family and his creation, Avacyn. Chandra, Jace, and Sarkhan, too, were present, and they all went elsewhere to pursue their own agendas (Jace found himself embroiled in the guild politics of Ravnica, too). The plane is ravaged, but not yet destroyed. It can be saved... if anything can stop the Eldrazi, that is.