Well I will summarise the material I have in my library on this line, note I don't necessarily agree with them, read the conclusion at the end.
Greet: The light squared bishop comes to e6, after a4 the queen may come to a5 and with Rfc8 and Nd7-c5 somewhere black often gets good queen side pressure. It's hardto summarise everything but he seems optimistic.
Interestingly there's also a note in his book that the move played by Caruana was called by Tsesarsky ''Dubious'' who gives the lines:
That said, Caruana's 13.Rc1 seems to be an improvement upon white's play.
Alburt & Dzindzi: In their book give 10..a5 an '!' and it as their recommendation. They don't cover the exact line played in the game with 11.b3 and 13.Rc1 but they are also very positive about the line, claiming the extra queenside space gives black ''more favourable endgames than the classical lines''.
Hansen & Nielsen:I couldn't find mention of the exact line here either, but they do mention a similar line, which may be possible to transpose into with: 10..Bd7 11.Rc1 and now ..a5 : the point being after 12.Be2 Bc6 13.0-0 Nd7 14.b3 Nc5 to transpose to a classical maroczy ''with white already commited to Rc1, which is not dangerous for black''.
So I think in summary, it is possible that Caruana's play is an improvement over the theory I have with me and may be very challenging. However, ..a5 as a general plan in the maroczy seems considered quite viable, so I do not believe it is a ''bad move'' unless Caruana has found a refuation.
This is Alejandro Ramirez' analysis of the Caruana-Carlsen game. Clearly, he believes that White's position out of the opening was fine, and he blames Black's struggles on his choice of the Accelerated Dragon.
EDIT: Here's the link
http://en.chessbase.com/post/sinquefield-08-streak-stopped-event-clinched
He could have had much better chances if he hadn't played the poor move 10.. a5. Regardless I think if the #1 player in the world is playing an opening against the world #2 in the highest rated tournament in history it just might deserve your consideration.
I'd agree with most of the above. Though since I didn't get an answer to my earlier question I educated myself a bit about Carlsen's chosen plan. Several authors have expressed quite positive opinions about the ..a5 ..a4 plan, so really I do not believe it is all that bad.