Commander 2013 is just a month away, and though there are known to be fifty-one brand-new cards among the five "arc" allied tricolor decks, only two of those cards have been spoiled so far. They're both new legends - Jeleva, Nephalia's Scourge is the blue-black-red one and Prossh, Skyraider of Kher the black-red-green one. The commonality between these two, besides being part of an apparent cycle of "tax-boosted" legends that get a benefit from the extra mana required to replay a commander from the command zone, is that they're both from old, well-known planes. Jeleva is a denizen of Innistrad and Prossh calls Dominaria home. In other words, this pattern will probably continue. So where will the other cycle members be from? Let's take a guess:
Green-white-blue: As I've noted before, this color combination is archetypally the most "group hug" style of EDH deck, with defensive effects that provide an abundance of life, cards, and mana to everyone at the table, then finishing with huge creatures that make little of that matter for your opponents. So naturally the most fitting new legend would come from the most feel-good sunshine-and-rainbows plane imaginable - Lorwyn, which, having been restored after the Aurora, is now a pastoral paradise. Perhaps a greater Elemental, a Kithkin, or a Treefolk would fit the bill here.
White-blue-black: Thanks to the influence of the Alaran shard of Esper, this color combination will forever be associated with artifacts. Of course, R&D probably doesn't want to explicitly reference one part of Alara and not the others here. So where else can artifacts with a color be found (other than, of course, Reaper King on Shadowmoor)? That's right - Mirrodin, now better known as New Phyrexia. A Phyrexian legend in these colors would make an excellent homage to the classic Ertai, the Corrupted.
Red-green-white: The flavor of these colors is maybe slightly harder to pin down, but to me it's always meant a sense of adventure, conquering the unknown wilds for fame, glory, and justice. Naturally, the plane that best fits these ideas is Zendikar - I'd love to see a new Ally legend here calling together his or her adventuring party.