I actually like the idea of Toffoli on the 1st line even better than the 2nd line.
Swapping Toffoli in for Penner leaves the 2nd line lacking on the forecheck and boards, and puts 2 straight-up shooters on the same line. The 1st line, though, things end up a bit more well-balanced. Swapping Toffoli in for Brown gives the 1st line a real sniper and, although Toffoli isn't a hitter like Dustin, J-Willie is good on the forecheck and Kopi is excellent along the boards so they should still be able to have some OZone possession time. Not only that, both of Toffoli's linemates are assist machines.
Even when Brown comes back I wonder if it wouldn't be a good idea to leave Toffoli where he is, stick Brown in Penner's place, and put Penner in King's spot on the 3rd line. I guess we'll see how it goes!