I think it will come down to a team getting desperate for Lane Johnson, and it just seems like CLE is in the spot to trade down. But if KC takes Joeckel or Fisher, and someone isn't in love with Johnson, it could happen.
Chase Stuart from Football Perspective has come up with a new trade value chart, that values top choices much less than the old Jimmy Johnson chart did, using the historical career performance of the players taken in those spots. If teams adjust their expectations, there should be more trades. But it's all about perception. GMs don't want to look like they are getting fleeced, even if they are really getting good value
http://www.footballperspective.com/yet-another-draft-value-chart/
According to this, the third pick is worth 18.4 points. Let's say you want to trade with SD at 11. That pick is worth 12.9 points. Would you be happy trading down to 11 and getting SD's 3rd and 6th?
I'm certainly not saying this new chart is somehow the end all be all, but I think it's better than JJ's old chart