I am pretty sure that it will be a surprise.
It's gotta be Clifford or Hagelin with retained salary. Lewis or Forbort if the Kings are open to retaining on contracts with term. Nobody else fits. Kings aren't likely to want to retain on such a minor deal, so that means it's likely Clifford or Hagline.
In order for it to be a surprise, it would have to be a bigger deal with Burakovsky going the other way, but that doesn't seem likely. It doesn't make sense to expect Burakovsky to go the other way, because why bother waiving DSP? I guess it's possible they are going to waive DSP, trade Burakovsky, and roll with a 22 man roster to stay under the salary cap, but operating that way could potentially get very messy for them.
Burakovsky+DSP+WSH cap space=4.957M of cap space as of today (a little bit more tomorrow)
So then it could be Toffoli or Martinez. Or with retained salary, Kovalchuk, Phaneuf, or Carter. Retained salary is unlikely, and with a tight cap situation Washington will probably not want to take on a big multi year contract for a declining player like Phaneuf. In this scenario, Toffoli and Martinez make more sense, but again I don't think this scenario is likely because it requires WSH to roll with a 22 player roster.