I just can't see Ramsey or Wilshere being dropped if every one of our midfielders are fit, even though that's hard ever.
Then again I can't see Coquelin being dropped neither. If Xhaka comes with such a huge fee will he be a squad player? Possibly but Wenger spending that much when it's so unlike him hints that he'll be a starter. I mean.. Wenger doesn't spend big much, so when he does it's for a starter.
I know Cazorla's contract is up next summer, but if he's here also next season and fit, is he not first choice CM? Can we really leave a player of Cazorlas ilk on the bench.
You can also make a good argument for Elneny.
All in all: The more quality in the middle, the better. No player should rest on their laurels and having a midfield of Xhaka/Ramsey/Wilshere/Coquelin/Cazorla/Elneny is a great thing.
Unless perhaps we're maybe changing formation, playing a more flat midfield trio.