I don't think that your proposed trade is what Los Angeles is looking for. Matt Roy is expected to take a permanent place in the Kings' defense and he's a couple of steps ahead of any potential replacement within the system, so we'd be loath to give him up. And as a rebuilding team, we aren't eager to trade away third-round draft picks. Meanwhile, Andreas Johnsson isn't much of an upgrade, if any, on Alex Iafallo and Adrian Kempe, and we also have Trevor Moore, Carl Grundstrom (with both of whom you are familiar) and Nikolai Prokhorkin at LW vying for playing time, which Johnsson would reduce.