If I thought he should move to 8, I'd play ESR for half a season out on the left in a squad role. I'd tell him to focus on covering his LB, cutting inside for 1-2s with the CF, and making late runs into the box. Kind of like how Ramsey played wide right. Could be useful in tight away games when rotation is called for.
I'm not as worried about the DM aspects of Xhaka's game for our future 8 as I am about their ability to cover the touchline and accelerate the tempo in tight spaces high up the pitch simultaneously. Emile is also quite physical these days.