Although we have no idea what is in Dragon's Maze this announcement set me off on some idle speculation.
Esper (WUB) Dimir/Orzhov Azorius
Raka (WUR) Boros Azorius/Izzet
Bant (WUG) Simic Azorius/Selesnya
Dega (WBR) Orzhov/Boros Rakdos
Junk (WBG) Orzhov Selesnya/Golgari
Naya (WRG) Boros/Gruul Selesnya
Ana (UBG) Simic/Dimir Golgari
Grixis (UBR) Dimir Izzet/Rakdos
Ceta (URG) Gruul/Simic Izzet
Jund (BRG) Gruul Rakdos/Golgari
Obviously staying open, taking fixing and going 4 and 5 color are going to be real options, probably the best option with at least a Guildgate in every pack of Dragon's Maze.
Some of the 3-color combinations look like they could punish 5-color greed, though, and it seems likely that most decks will at least be two colors with a sizeable splash. Naya aggro or Boros into Rakdos with Orzhov removal and Stab Wound. Grixis looks like something you would never do without opening bombs.