I think I've seen the "Nylander at centre" experiment enough times by now to make me believe it would never work as a viable long term solution.
We paid this guy $11.5M to be a 90-100 point winger. There isn't another 2C in the league making $11M. If the Leafs put Nylander and Matthews on the same line, and trade Marner while eventually replacing Tavares, they will rebalance the forward lines with a traditional setup and can use the rest to put towards defense and goaltending.
Whether that happens this year or next year is up to Marner and Tavares but it will happen eventually is my guess.