Don't see any reason why Detroit would trade Slay. He has a $1.7M cap hit in 2016 and is only 25 years old.
I don't think Detroit views themselves as needing to rebuild I think they believe they can contend in 2016 with some minor changes.
Is firing Caldwell a minor change?
If we get both McCourty's together, will one be able to change into an animal, and the other into a ice/water based object? That could be useful.