I don't think the Penguins are in a rush to sell any of these guys, unless they get a crazy offer for them. The thing with trading EK is that you could possibly get better value for him by waiting than trading him now, since the cap will be rising more, Karlsson will have less term and Karlsson could go on a hot run to increase interest.
Rakell should 100% be traded this off-season, they should sell high on him. Beyond him, I'm not seeing anyone that is a "trade immediately" type of guy. By mid year next year, I'd like to see McGroarty as Crosby's LW and Koivunen as Malkin's RW.