I like the idea of Nylander playing center. That actually really solves a lot of our problems going forward.
I also think that if we actually run 4 lines, there's no reason the 3rd line C can't be a quality player. Kadri might even be more effective on a third line because I think his game is much better against weaker opponents. IIRC, Kadri was on the third line during the short season where him and Frattin racked up all those points behind Bozak and Grabo.
It also depends on whether they think they can sign someone like Stamkos. If they want to go with Stmakos - Nylander - Holland - Gauthier ... then there's no room for either Marner or Kadri. (Babcock might even like Bozak as the number 3 going forward).
For this coming year, I think Marner should play center in the OHL because that gives him a greater chance to dominate down there. But I wouldn't mind if we got the coach to play him for 1/3 of his games on wing too. Even if he plays center in the OHL, there's no reason he couldn't shift to playing wing when he plays for the Leafs or the Marlies.
Ultimately, I think it might be better to have Marner as a winger. With Kessel gone, we're pretty weak on RW.
Our two best forward prospects by a mile are Marner and Nylander. It might be a good idea for those two to be line-mates going forward and hope they develop some chemistry. And from what I know about about these two players, Nylander will probably make a better center than Marner.