I think it is pretty obvious the Leafs have to do one of 2 things:
Option 1: Move Nylander to center full time
Option 2: Re-sign Bozak to a short term contract which effectively keeps Nylander from moving to C for its duration.
They need a #2/3C after Matthews and Kadri so they either need to re-sign Bozak, convince Stastny/Thornton to come to Toronto on reasonable contracts, or find somebody within the oeganization. If they go internally, it is a much bigger risk to go with a rookie #3C (Lindholm/Aaltonen) over a proven young NHLer with faceoff and center experience. Especially if their current plan for #4C is one of these rookies.
Edit: If they decide to move Nylander to C, they need to find at least 2 new wingers and a 4th line C to come in (UFA, Leivo, or Marlies). If they re-sign Bozak, they just need 1 winger and a 4th line C.
Current wingers with Nylander as a C:
Hyman, Marner, Kapanen, Johnsson, Brown, Marleau - These guys are not losing a spot to start the year IMO unless we make a big trade that changes everything.
Defense is a little tougher to determine as we need to decide what capacity Hainsey will be used in this year so he doesnt get burnt out and how quickly we want to push Dermott up the depth list. Also because we should be focusing on improving here most and trades could be made.