I've always been against stacking the top line but...I find myself wondering if Berube should just put Nylander with Matthews and adjust the rest of the lines and see what happens. Nylander is already spending a lot of time there anyway. It doesn't look like Matthews has the ability at this point to drive a line by himself, whether due to injury, wear and tear, mental issues, whatever. Maybe putting the two of them together would be a case where they produce more together than their two lines do separately, or maybe it rejuvenates Matthews.
If it's a nagging injury then it is what it is and none of this really matters.