I can see 3 at the back working for us with wingbacks, in fact given the lack of a really standout central defender and a standout defensive mid, which I think is nesc to play a 4 man defense, I think it will make us defensively more solid and harder to beat like Holland at the worldcup. I think with Jones, Smalling, Blackett, Rojo, Shaw, Rafael we surely have the foundations to make it work.
What I can't see working for us is 2 strikers upfront with a number 10 behind them. I think it just makes everything to narrow and the biggest threat comes from counterattcking, which simply won't be very effective without pace upfront. Rooney, RVP and Mata is just an attacking lign up that lacks pace. In fact even for Holland I think it wasn't working and they had Robben there to provide them with pace, I always found they were struggling offensively in that system and things only started happening for them when Robben was allowed to play from the wing and Depay or Lens was brought in to play on the other flank.
That is why I wouldlike to see us move to a 3-4-3
It will mean putting one of RVP or Rooney on the bench, or playing Rooney out of position on the wing which isn't his best position at all. It also means no real number 10 role in the system so Mata will have to play more on the wing and Kagawa will probably become useless for us. But it would work brilliant for Di Maria, Januzaj and also Lingard I think.