If we move to a 433, Di Maria can play in the front 3 or the midfield 3. Given our squad composition (with its strong options for the front 3) a midfield 3 of Herrera, Fletcher/Carrick (or Vidal or even Blind), Di Maria would be an obvious option. In a 442 he can play on either wing or in behind the striker in the centre.
He's not only a high quality player, he's a hardworking player and he's a flexible one. If we buy him, it will be Ancelotti's problem, not LvG's.
Of course, like every other player you do have to put a value on him and that's a much harder question. To me at £50m he seems like a fair deal, at £60m he sounds expensive - but that's me, my mileage and other people's, or United's may vary.