Both different types of players, though. Actually, we could do with both.
Jorginho is more a holding player, and would rotate with Matic, whilst Seri is more an 8, who links midfield to attack. The both could play together.
Pogba Seri
Jorginho
Very much doubt we'd see that, mind. Jose likes a bit of height and physicality in his midfield.
Either way, with Carrick retiring and Fellaini looking likely to leave, we need two midfielders.
A holding midfielder - Someone to rotate with Matic.
A playmaker - A number 8 who can control the game from deep, but can also play as a more advanced 8 if/when Pogba is injured/rested.
Seri, Pjanic, Wilshere, Thiago, Modric, Gundogan, etc. Players of that ilk.