I think theres definite partnerships that Ole is looking at developing... Pogba linking up with McTominay, Wan Bissaka and Rashford primarily. But also 2 games in a row that Greenwood has been that other guy starting from the right alongside those, and while he might not start the season as a regular there, can see him finish it as one.
Martial has so far been the 2nd striker, but I think come the season he'll start on the left with Lingard/James/Mata starting on the right. Makes sense for now having Rashford/Martial separate as you don't want to just throw Greenwood, Gomes, Chong and James all in the same side without more experienced heads, so Martial is the starting caliber striker to help out Chong and Gomes(same with Lingard).