I have been saying for ages but I think Fellaini could be effective as a 9 in this system.
Ordinarily (eg last season) I was very much opposed to having him up front, and thought he was best deployed alongside Herrera as advanced box-to-box midfielders, with a holding player behind them.
In the current system however, our #10 has mostly been playing almost as a second striker, rather than a playmaker. Additionally, the wide men act as inside forwards. All three players behind the striker therefore are (or should be) making runs, overlapping and basically - scoring goals. In this system, I think some of the key attributes you look for in the striker are the ability to hold the ball up, the ability to bring others into play via flick-ons, and the ability to press the opposing defenders. Fellaini is very good in all of these areas.
What I dont want to happen however, is what happened against Swansea, which is that as soon as Fellaini was on the pitch, we abandoned all efforts to actually play the ball, or work the ball into good crossing positions (what we had been doing for the majority of the game) and instead started lumping it up from anywhere on the pitch. If we are planning on doing that then I would rather just play with 10 men - and I say that as one of Fellaini's most vocal supporters on here.