I think more likely he will play e4 and we'll get a Sicilian...
Should Carlsen go for the Orangutan tomorrow?

More likely sure, but think about Carlsen's position: a draw with white wins and a loss wouldn't be the end of the world (although a clean sheet is pretty). Chances are very slim that he'll be able to play anything he wants without immediate dire consequences in a WCM again. I say go for it. Play the Halloween Gambit.

lol...I want him to play Benko Opening 1.g3 .
Much less exciting. He played the Réti KIA in the first couple of games as White, and 1.g3 would just lead to a transposition of that, almost certainly.
A Catalan would be nice, and perfectly appropriate for a WCC level game, and a Reversed Dragon could be quite cool if they play according to Dragon theory for a while. Magnus has played the Dragon (itself, not reversed) 6 times in serious games, if I recall correctly, so such is not unthinkable. I certainly wouldn't bet on it, though ;)

Anand won a very nice game in 2008 with black against Carlsen in the open Catalan I believe. That pawn sac to obtain the centre always gives exciting play. Of course Magnus is lot stronger now than he was in 2008. Maybe time for revanche?
He has three games to get half a point. He'll manage.
He is in the extremely luxurious position to having the option to play any opening there is - in a World Championship match.
It might be insulting to Anand, but if you forget that part, how awesome would it be to see a crazy surprising no prep wild clublevelopening but high class struggle?!
Think about it.