Well Pep changes formations readily, so I don't think it's a stretch to suggest we may well play with 3 in midfield at some point.Your assuming we will play three in midfield
Delph and Fernando have been good enough as part of partnership with an inform Yaya or Fernandinho So that means only one more
If we play 2 in the middle could we really get away with three of starting quality and two back ups ?
I cannot see us getting rid of two midfielders who we have really only just bought and one of which is home grown
Delph/Fernando for me aren't top class midfielders. They're both decent midfielders who could be solid backups - but would you put them alongside the teams we want to compete with? Kroos, Modric, Iniesta, Busquets, Rakitic, Thiago, Xabi Alonso, Vidal etc. They're a step down I think you'll accept that.
Even if we only play a 2, I don't think having Fernandinho (31 next season) + Gundogan is enough depth, we'd need at least one more of similar quality. So I personally think we need at least 2 CM's; seems like one will be Gundogan which is a great start, but hope we get another in.