Okay, so the second season is on January 2010, and you've got no idea on how the story will go... Well, here's the result of my brainstorming:

Report says that the planned plot will take place right after the events of the last episode. Apparently, Sebastian has lost the seal of the contract when he lost his left arm during his last battle with the angel Ash. It was said that because of the loss of his seal of contract, their Faustian contract has become void. Sebastian didnt have the chance to eat Ciels body and soul. From here on, the story will continue, though there is still no vivid idea of how the plot will revolve. A rumor said that Sebastian will get a prosthetic arm, opening the "Noah's Ark Circus" Arc. Another rumor also stated the plan of making Sebastian a human, but how the story will make him one is the main issue for Yana Toboso-sensei.

Yeah.. so that's how it goes...