I don't think Kassian would be a bad addition at all. Add some nastiness to our butter soft lineup. And he's right handed, always an incentive.
There are a bunch of guys that I think might add things we're lacking.
I think guys like Kassian, Mason Raymond, and Jamie McGinn can be good additions, slotting in the middle 6 with the potential to get better.
Any idea of what Nashville might want for a guy like Craig Smith? He's still young, but I think he might be a good 3rd-line guy, and he can play center or the wing. Slot him on a 3rd RW with Miller at Center. If we could trade for and negotiate with Stastny...
Pure speculation/fun on my part:
Kreider - Stastny - Nash
Zuccs - Stepan - Kassian
Hagelin - Miller - Smith
Pouliot - Boyle - Dorsett
McD - Girardi
Staal - Stralman
Moore - Allen
That leaves 5 million in cap space for resigning.
Out: Brassard, Del Zotto, Pyatt, Moore, Pouliot, Cally, pick/prospect (?)
In: Smith, Stastny, Kassian, pick/prospect (?)
Why: Colorado wants a young defenseman. Package DZ with a guy like Moore (RFA, UFA) for a UFA Stastny. Add a pick as necessary. Colorado gets their d-man and a center to take in a bottom 6 role who can also PK and such. Might not want it, but it might be reasonable enough. Leaves the top 6 center positions open for Duchene and MacK. I'd like McGinn, though I'm not sure what would need to be added. I'd be open to moving Girardi, but then NYR would need a RHD coming back alongside everything else.
Nashville I'm not all that sure about a justification. I just think a guy like Smith would be a good fit for a Rangers bottom six and would like to make it work. Nashville gets (arguably) an upgrade on Smith in Brassard, though Smith is on a better pace than Brassard this year. Throwing in a guy like Pyatt gives them some extra size they're currently lacking. Not sure if they'd want it.
Vancouver--Torts gets Cally back. Rangers get a nice power forward style player with some nastiness in Kassian. Adjust the lineup as necessary as the players are fairly versatile.
Could still move Girardi/DZ if wanted. Though there would need to be nice returns to facilitate that and fill their spots.
That would (currently) leave us with about 10 million in cap space pre-resignings and pre-cap rise.