Given that we're committed to developing Frank over the long haul, the Jack/Ntilikina tandem seems perfect this season.
I think the easy opportunity is upgrading the SF position. At the moment we don't have a SF of the future at that position lined up - or a 3 and D player to play some adequate minutes. Seems as if the Knicks are hoping for McDermott to grow into that role, as he's the closest thing we have right now.
Kanter might be a less rounded player vs Willy, but he has an elite post up game (61% FG) that it clear to the coaching staff how they want to use him. His rebounding has been prodigious (almost 16 rpg per 36 mins) thus far. It's tough to argue for minutes for Willy when Kanter's been tremendously efficient.
What to do with Willy, Willy seems like much more of a complementary player. Willy is basically a solid, prototypical center on offense, above average on a lot of skills, passing, rebounding, scoring. He'll put up numbers within the flow of the game and get some easy buckets by moving without the ball, but teams won't alter their game plans to stop him and doesn't create a defensive vacuum that creates better spacing for his teammates. His contract is a bargain and I can see him being a productive player elsewhere.