Last year it was given to "Protesters." This was mostly for the Arab spring, but also the Occupy movement. I doubt that they will go back to the Arab protests for another Person of the Year.
I'm guessing they will go with someone or something that nobody expects. They will try to make a weak political statement by being non-political and very centrist. That way they will try to not alienate either the US right or left, but try to make a feel good story that the average USian will be OK with.
Rarely is the Time POY not an American. More often than not it's someone from government, or with a political edge (The Protester in 2011). And the person/group has usually been a major news maker or someone behind the scenes of the major news of the year.
So, here are two possibilities:
The Changing Face of America (or of the American Electorate) Nate Silver