That'd be my only concern if we get Pogba aswell. It would seem like Pogba and Yaya would be fighting for a place alongside Fernandinho or Delph who would be doing the same. Putting the two in alongside one another would be tactical suicide.
Don't get me wrong there will be a hell of a lot of games to be played so they'd inevitably get more than enough minutes but who's no.1 in the biggest matches? Would we spend £70m on a lad and then have him as Yaya's backup, or do it the other way around, buy lots of cake and hope for the best?
That's what I worry about as well. You definitely can't play Pogba-Yaya as a midfield 2 in any semi-serious game, Fernandinho or Delph needs to be there to give it some semblance of defensive stability. So either you bench the £70m+ signing (not going to happen) or you bench Yaya - likely to make him unsettled and also insane given his wages etc.
The other option would be to go 4-3-3 and that means dropping Merlin (not going to happen) or a £50m signing in either De Bruyne or Sterling.
It's going to be a managerial nightmare unless Yaya knows he's likely to be on the bench a lot, and knew that when he decided to stay (I seem to remember he was 90% likely to leave at one point according to his agent).