The next cape obviously needs something symbolic on it. It will probably be simple. Colors, probably either yellow or green, because those are major colors which are unused. What else is symbolic and simple in Minecraft? I'd have to say the next thing would be a grass block, after all it is the icon used for the game pretty much everywhere (The game, Minecraft.net, Minecraft forums, etc...). A grass block would be difficult to put on a green cape because of the fact that grass is green, so it will probably go on a yellow cape.
TL;DR, I think the Minecon 2013 cape will have a grass block and a yellow background.
Minecon 2012 cape was a Curse logo no a pickace :|
I hope the go with a whole new cape. Using the third most wanted cape is also using a cape most people didn't vote for. Next year will they get a cape NOBODY voted for, simply because it comes next in a pole they did two years ago?