Besides Asamoahs goals this season, you don't actually see him attacking often and being aggressive like an offensive winger would do. He rarely leaves his position to throw himself in the attack.
So I think Isla is a perfect match to him. Litch is so great defending, but not that good attacking. With isla we can have a very dangerous right side. And once in a while Asamoah can do his thing on the left side.
I mean, against Chelsea it was clear to me that we severely lacked plays in both sides of the pitch. The midfield was supercrowded by both teams and Asamoah even cut inside everytime. We needed an Isla there to get some quickness and aggressiveness.
Also, as you have a very mistake prone player in Bonucci, and a player who just can't leave the starting team in Litch, to me Isla in the wing and Litch as a RCB is a must try.