Who knows and only time will tell but I don’t see Domi playing C; he has impressed me with his playmaking but defensively - he’s atrocious.
My guesses as to what Keefe will do (question marks means there is uncertainty):
Domi? / 34 / 16
Bertuzzi? / 91 / 88
Knies / Kampf / McMann
Holmberg / Dewar / Jarnkrok
Reaves (physicality) & Robertson (offense) are the spares

That bottom six worries me but if they can tread water against BOS/FLA I'd be fine with it. Domi at C gives them 3 legitimately great lines and they'd probably just outscore their defensive problems. Plus, they'd face weak opposition as the third line

That third line just cannot be trusted to play in their own end. Bertuzzi-Matthews-Domi has looked very good. Putting Nylander on a third line with Holmberg and Knies/McMann could be almost as good offensively as the third line you proposed while still being solid defensively. Then you'd have McMann/Knies-Tavares-Marner. I think you have 3 lines that can defend any line and score against any line. I like that.

We have the personnel to have a 4th line that can shut down top competition and take important defensive zone starts: Dewar-Kampf-Jarnkrok. You don't need JT in a shutdown role, nor should he be.