Barkley is pretty poor imo, and although Koeman is probably going to play the 'he won't sign a new contract' card, i reckon he thinks the same.
Sigurdsson is a far better player than Barkley will ever be. Plus, given how the PL works, Everton will more than likely be able to command a vastly inflated fee for Barkley.
Good bit of business all round.