Never gonna happen really, is it?
1). He might not have cemented a first-choice place, but he's featured in 22 apps out of 30, so he's a regular player in one of the best teams in Europe and hardly some unwanted fringe player like Onuoha.
2). Man City regularly rotate players, as do most very big teams, so it's not like he's being left out
3). He could grab himself winners medals and all sorts at City
4). If any team isn't going to need to sell a player, it's going to be stupidly rich Man City.
One thing I've noticed about Man City is that they have a thing for at least a few top English players. Hart, Richards, Johnson, Milner and so on. Johnson could end up being a key feature of the future England squad, so I really can't see Man City wanting to let him go at all.
PS: Just before anyone thinks I have the anti-mackem bias, I don't think he'd come to us either, at all.