I actually think that in future you could see a narrow 442. Sancho can play on either AM side with Bruno, as Rashford partners Greenwood ( who ends up taking more of a second striker role). Rashford isn't a good lone striker, but in a front 2 he's deadly.
At the moment, Sancho clearly goes right. I think Cavani ends up starting less because Greenwood starts to shine as a 9. Martial covers those positions until he leaves( so will start the season on the left), until raahford comes back.
Solskjær is reportedly thinking of using a 4-3-3 more this coming year if Varane is signed. With Sancho's signing, I doubt that we will see as much of Pogba playing as a left-winger. My guess is that to start the year, we will see Sancho - Cavani/Martial - Greenwood as the primary front three. Cavani will get some rest to be saved for the Champions League and towards the end of the year. I think Amad will get a chance to contribute, and if he is able to do so effectively he will stick around all year. If not, he is likely to go out on loan in January. His presence at the Olympics probably dictates this as much as anything. I don't like seeing Martial on the left. I don't think he is effective on the wing, and I think he allows himself to become discouraged when playing on the wing. We might even see VDB in one of the forward positions in some matches.
Rashford will regain his place on the left, and Sancho will move to the right. Then, we might see more of Greenwood at CF.
I like to see this but doubt we will play them together much this season. Diallo is still too young and hasn’t been developed physically, while Greenwood is still not fully ready for no.9 role yet with his lack of hold up play and movement. They both need more time.