Why can't you have a number 10 role? It's just a variation of 433 with the point of the midfield three pushed behind the central forward. You can do what the fuck you like with any system. I'm sure someone will call it 4213 or whatever, but it's all bollocks, it's just a variation of the set up.
As for Sterling, in the first part of last season he was excellent at times and didn't look out of place for England, suggesting he isn't good enough at this stage to push for a place for Swansea is bollocks, he's good enough and has a season behind him now. I think it'd be a good move, but it does leave us short on cover.