While it is nice play, hes not much of a ball winner. Neither does he have the physicality that sees Matic and Fellaini selected as our DM and not Ander.
So if we played him as our DM you can expect to see Fellaini or Matic selected in the same lineup while Mourinho is manager. Alternatively he might be pushed into a normal CM role rather than a DM one.
Also we're talking about a league where statistically Daley Blind is performing just as well as him and was better than him against Germany. Perhaps that also says something about Blind being underused and underrated, but considering Mourinho wasnt keen on giving him many chances it doesnt fill me with confidence that he's such a great player that he could overcome Mourinho's stubbornness to stick with physical players.
Look at Fred, we paid a lot for him, he finally had his best game even getting on the scoresheet and then he's out of the team. What would be so different with De Jong?