I like the idea of dropping Rooney, but Pogba isn't a number 10. You'll come up against the same issues of undisciplined play. One of the issues with the 4-3-3 we saw against Feyenoord (first half) was a lack of support for Rashford up top. If we play a number 10, whilst it's a semi-free role, the idea is that there is some support for the strikers. Pogba doesn't play that far forward generally, and will just roam wherever he likes, which often (as we've seen [at least until he gets some experience]) will often be the wrong place.

I would also say that Blind should be in defence. There's clearly some issues with his physicality, but since he's been dropped we've practically lost any build-up of attacks from the back line. See Kolarov versus Bournemouth for an example of the benefits of a centre back with passing ability and time on the ball.

It's a shame Schneiderlin isn't taller, because Mourinho clearly prises height. But also, it should be noted that in your chosen 4-2-3-1 system, Fellaini actually played very well. It was only when we switched to 4-3-3 and he was asked to play that holding role on his own that it became problematic. He's not ideal, obviously, and I wish he wouldn't commit silly fouls all the time, but, his height does actually help the team significantly. If he's not getting on the ball from set pieces, he's dragging defence away from the others that do.

It seems then that the only players who don't benefit from 4-2-3-1 are Pogba and Herrera (because he won't get in the starting line-up). But, it suits Fellaini, it's suits Mkhitaryan (who's not a wide player, despite playing on either side of a striker, and won't operate well in a 4-3-3 as he doesn't play wide enough and isn't the fastest. He should be starting in the number 10 position, replacing Rooney.

Basically, Pogba needs to learn how to play in a two, or forever be associated with the Yaya Toure-type irresponsibility, which would be annoying, given his fee.

I'd go for:

De Gea,

Valencia, Bailly, Blind, Shaw,

Fellaini, Pogba,

Mkhitaryan,

Rashford, Ibra, Martial

Not ideal, but the best option we have at the moment, I think. Dropping Rooney is a must.