Well, took them a while, and stil, if Bale was fit, the 433 with the BBC would be their first choice, no matter how good or superior the 442 has been for them this season.
They basically needed evidence that they needed Casemiro after the fiasco of playing Kroos as a DM with Modric and Isco/James in the midfield but in a way they keep finding ways to shoehorn players, the 2 basic points are that Casemiro plays as the DM and Modric is the brain, with that premise they can basically throw in any player they have in the remaining 4 attacking positions because they're so good it will work.
I also think Pogba is the best guy to build around but never as a DM and that role will be critical, it depends if you go for a 4231 and 433 with 2 DM or 1, if you throw a single guy there, you need someone really good, like Kante good as he will need to cover almost two roles, if Herrera gets a chance to build a DM duo (same role Khedira did at RM) then you can afford the luxury of getting a more limited player, basically a destroyer with stamina, strong, kinda tall and who can put a 3 meter pass 90% of the time, finding a player like that won't be hard when you can surround him with at least 3 good players who help him.
James is worth considering because there's not many players of his caliber for the taking (and at what could be a discount, too). He's no what United craves, but if the market doesn't present great options in other positions, then it would be wise taking a chance on him