I don't see it to be honest, I put Osman in the same category as Arteta and Pienaar, obviously not as good, but he's a technically gifted footballer. Good Touch, excellent close control, the ability to twist and turn and create space for himself in tight spaces. Even then, he just about gets away with it. Cahill is by no means a bad footballer, he's decent with his back to goal, and has an underrated ability to see a creative pass, but that's as far as it goes really. He can be a powerful runner, but he's not going to run past a fullback or get into his stride with an opposition wide player and fullback tracking him.
He's actually played there before, when we had our injury crisis last season, him and Gosling outwide was quite difficult to watch, both players trying to pass as half decent wide players, and they struggled. You have to take into account the lack of pace and dribbling ability we already have, using Cahill outwide wouldn't solve anything really.