I thought he would thrive in Flick's football, but it's tough to imagine him starting over current form Casado and Pedri. Olmo is our most attacking oriented mid who should start when healthy and then there is Gavi/Fermin and lastly Bernal.
De Jong is a different kind of well rounded mid. I'd love to keep him, but someone's playing time has to suffer greatly, and it'd mostly likely be Gavi. He just doesn't offer anything in any of those three roles better than the others can. He will also need to learn how and when to press, vs running around randomly and leaving holes in midfield everywhere.
One thing is for sure, De Jong's intensity and pressing needs to improve in order for him to earn his spot. I don't care how good he can be, he's got to run. He's been out for 6 months with a nagging injury, so I'm willing to accept that he might be off due to that. That excuse won't last long though.
