Based on the players we're linked with it seems like we're desperate for CMs. Can not understand why we would be, with Wanyama, Dembele, Dier, Winks, Onomah, (Eriksen, Sissoko, Alli) ready to dominate all other midfields out there.
Because you can't rely on players to get through 48 games per season, so you need rotation players and then backups for those. Dembele will be 30 at the end of the season, and isn't normally capable of playing 40 odd games in a season, so you have to plan for the future and a contingency.
Even if Winks is the future, you need to give him competition.
Take into account our 5 man midfield (in a 4 2 3 1 formation):
Wanyama (Dier) / Dembele (Winks)
Eriksen / Dele / Son
Sissoko isn't staying, and so that leaves Onomah to rotate with the forward 3.
Firstly, he's not 3 men. Secondly, he's not really 'ready'. Ideally we'd probably have Edwards/Onomah rotating with Eriksen, Dele & Son - but we'd need another 2-3 players who are capable of stepping in when ready, too. It's pointless to sign "squad players", so we seem to be targetting younger players who could step in and do a job. That's where I think Barkley makes sense.
Hard to include Lamela in the above considerations, as we don't really know if/when he's coming back, and then how long he'd be fit for.