I have been advocating this for a while now. He is the best target #9 we have by far and that is so important for a counterattacking team. And its always been so important for Mourinho just that.
It would also give us a presence in the box, when in possession, which was severely lacking yesterday. I thought Alexis did well, and the attacking trio of yesterday might work really well when we are dominant in possession; but we will never be under Mourinho against an equal or better team. Then Fellaini is the better choice.
Fellaini has a damn engine on him as well and would probably be able to do as a good job pressing as Alexis does. Or at least try to. Lukaku is to heavy and does not have the stamina for any team that does some form of pressing. He is similar to Zlatan in that regard.
Let Lukaku work on his hold-up play in training and for now fight for a place at RW.