As a Wings fan who is a huge fan of Dekeyser, and who sees Tanev as a Dekeyser Plus, I would fully be on board with trading both guys.
Maybe it's the Wings fan in me speaking - the one who waited for a Peak Brad Stuart to complete the Wings puzzle and a Prime Niklas Kronwall to hold down the 2nd pairing of a should-have-been back-to-back Championship team. Maybe it's someone who has grown to notice the nuances of hockey after watching two decades sort of hockey. But either way, Tanev isn't the bottom-brick guy. He's an add-on.
In other words, Tanev isn't going to be the first guy people point to on a Cup team. He's not going to be the Conn Smythe winner. He's not going to be the team's identity. What he's going to be is the missing piece to an already assembled Broadway-calibre cast. He's going to be the steady second-mate to an All Star boss who is so dynamic that he takes turns playing hero and villain season-to-season.
I get that he has beautiful advanced stats, but Vancouver should be smart and profit from that hype if the profit is to be made. That's not to say Tanev should be on the block unequivocally, but if the Larsson/Hall market is there, as a rebuilding, upstart, or no-man's-land team, the chips should be in the table.