Even a False 9 would get the best out of Martial, Alexis and Rom.
Martial hugs the left side a lot more than Alexis, make sense he starts on the Left and works well with Pogba.
Playing Alexis down the middle allowing him a free role as he will make the runs in behind and will drop back to tackle, play him as the false 9. Rom imo is absolutely lethal when he roams to the right and goes at the LB/CB, I think he prefers it when the ball is played in behind for him to run onto, like Vs Bournemouth for example. He can position himself in between the LB and CB and whoever picks him up will leave gaps for Sanchez.
Could work, doubt it will ever be tested but would be interesting to see.
Martial ------------ Lukaku
Alexis
Pogba Matic Herrera
Sandro Jones Bailly RB
David