Instead of who? Silva? De Bruyne? Sterling? Sané? Foden is promising but do you really think it's fair to expect him to do as well as any of those four players?
Right now we have a 24-man senior squad.
Two are goalkeepers, that leaves 22.
Four (including Delph) are fullbacks, that leaves 18
Five are centerbacks, that leaves 13
Two are out-and-out strikers, leaving 11
Two are defensive-minded midfielders in a role Foden and Diaz can't play- that leaves 9
Sané, Sterling, Silva, De Bruyne, Gundogan, Bernardo, Zinchenko, Foden, Diaz
In the average City line-up there's room for four of these players in the starting XI and maybe two in the bench. So three must miss out. Zinchenko, Foden and Diaz are the obvious choices.
It's not that Pep doesn't want to give them a go- it's that he can't do so without dropping one of the other six, who are all talented and deserving. It's not like we're playing Sam Clucas and Charlie Adam instead of giving youth a chance, these are world-class players.
So when will their time come? That depends on three things: how many dead rubber games we get, cup draws and injuries.
- They will get a chance if we wrap up the league or UCL group stage/tie with games to spare (not saying I expect that to happen)
-They are more likely to get a go against Rochdale than Chelsea in the cup, or Basel than Real Madrid in the Champions League
- If two of the aforementioned six get injured there is room on the bench for Foden or Diaz.
Diaz can play as a striker but I don't think he'll do that for a while under Pep.