I think Blind will probably stay at LB for the time being.
Strootman for some reason hasn't looked great in Oranje, while Wijnaldum looks like a lost pedestrian when playing in front of defence. Vilhena I don't think is up to it at international level. Only El Ahmadi hasn't looked completely out of his depth in Feyenoord's midfield in the Champions League campaign so far.
de Vrij - Hoedt -Van Dijk
Karsdorp - Wijnaldum - Propper? - Strootman - Blind
Locadia - Promes
Reserves: Vorm, Depay, Dost, Klaassen, Kongolo, vd Beek, Tete, Pieters/Haps, Berghuis. Lack a good holding midfielder and a good striker
Kongolo and Klaassen aren't playing at their clubs. Hope they do sometime soon. I'm worried most about Klaassen because if Koeman doesn't even play him?!
Kongolo could still go on loan to a good Ligue 1 club like St Etienne or Bordeaux. Become a good CB there, before returning to Monaco.