I am confused with the Morozevich variant. I've seen quite a few funny games where they played ...g5, which gives very interesting moves, but I'm surprissed at not having seen any game in which white plays 4.e5, which seems a natural move, blocking the classical square f6 for the king-side knight. Here, What is the main idea of the Morozevich variation in the French vs. the Tarrasch?, Nh6 was proposed in a comment, but I think after Bd3,c5,Ndf3, the black knight is quite weak. How would you play against 4.e5?
I don't think Black is in a hurry to develop the knight. 4...c5 is the main move. If White plays Qg4 the bishop goes back to f8. As a matter of fact the bishop sometimes goes back to f8 even if White doesn't play Qg4.
Of course Nh6 is fine and the knight will then go to f5 where it is happy.
Note: 1. There are other lines where the Bishop returns to f8, like 1.e4 e6 2.d4 d5 3.Nc3 Bb4 4.e5 b6 5.Qg4 Bf8. 2. In non-Nf6 lines it is common for the knight to head to f5 via e7 or h6