Well that’s just it. Pittsburgh is screwed in a couple of years regardless. Crosby is 35, Malkin 36, and Letang 36, and they have no top prospects coming. They likely have no fear about the last 2 years of Karlsson’s contract, because they know they will be rebuilding anyways.
In fact, they might be the only team that would do it with little retention. If they can send Granlund and Petry back in the deal, that covers nearly the entire $11.5M for the next 2 years. If they get just a couple mil retention, they can field a 22-man roster and be under the cap.