To me, this was the most obvious ship while watching the movie.

Well, save for two things: 1) his devotion and guilt to Mal pretty much ends Cobb/Ariadne before it can go anywhere and 2) if you interpret the film as having more than four (? I lose count) dream levels--that is, Cobb never emerged from the first deep-dreaming escapade--than Ariadne isn't a real person so much as just a projection of Cobb (c'mon, she's the only character who is persistant as to Cobb's emotional problems and she is a better (younger, more aggressive) architect than even he was?).