I know that we are looking to acquire some youth and the Coyotes are really making a push for the playoffs. It seems like Cullen would be a good fit, as his cost is low and he adds some scoring that Phoenix expected out of Mueller. Cullen for Mueller and a 3rd? I don't know that Cullen's cost is low enough for Phoenix since they are financially strapped and I think still officially being operated by the NHL.
I think Mueller would provide a strong young player that we could further develop. He had an outstanding rookie season and has tailed off since. However, he hadn't really had much developmental help as Gretzky was seemingly occupied with his financial holdings in the franchise in the last year or two of coaching. Mueller has the talent to turn his very young career around, which is apparent by what he did his rookie year and where he was drafted.
This is obviously written in theory as for all I know the Canes don't have any interest in him, but I do know the Coyotes are trying to make a strong push to the playoffs and Mueller is subject to recent trade rumors.