I agree Kramnik will probably be the next challenger. Maybe Aronian, or even Anand. But I think Anand can handle them.
Down the road, Carlsens biggest threat is going to be Caruana, I think.
One of the young 22yo below with 2650+ rated grandmasters are potential challengers.Maybe So, Giri, Caruana,etc.
yea l8er caruana
After Carlsen lays the smackdown on Anand, Caruana will win the candidates in 2015. Then lose to Carlsen.
Mostly caruana, aronian or kramnik.
Carlse- kramnik or carlsen - caruana will be intresting. Kramnik is very tough. Caruana is high rated.