Talk about future, if 4-3-3 formation is continue to be used, then between Lukaku and Rashford, only one should stay in MU.

Rashford is never a winger, not to mention Lukaku.
Both can only perform when they are in CF position.
Look at Rashford during Southampton match, look uncomfortable, under perform, just like old days during Mourinho era.

But Lukuka is even worse if being put on winger position, that's why Ole choose to sacrifice Rashford, but that's not gonna work.
Since both won't satisfied being use as 2nd choice, we need to sell one.
And it is no-brainer to sell Lukaku.

Remember his long goal drought even during Mourinho era, even being used as CF in every match?
He is not consistent enough + slow to be MU 1st choice CF.
He is strong in physical, but we need a striker with speed to match with the whole attacking style of MU.