Witsel is a CM that would be inferior to all the current cm's.
He is an inferior CAM compared to Pereyra
Dennis Praet on CAM with Pereyra on CM, costs far less, and is a stronger team then one that benches any of two mentionned players for Witsel.
Witsel plays for our NT cause he's a complete CM that is decent at infiltrating offensively. I personally prefer Nainggolan+Fellaini+De Bruyne(cam) with Mertens and Hazard on the wings. He plays cause Defour didnt quite reach his potential, dembele is a liability at cm and Simons is to old. When Praet and Tielemans come to maturity, he'll very easely hit the bench forever. Nainggolan+tielemans behind a randomly chosen trio of : Hazard, Praet,De Bruyne, Januzaj, Chadli, Mertens.
This is not the Belgian NT , this is Juventus. Unlike Belgium we got more then 1 worldclass CM, we got 3.
Witsel has no place at juventus, other then a bench player.
I agree with @chester that its a far better idea to get Praet and Tielemans. Most interesting young talent in Belgium currently.