On Kessel, I am not sold on trading Dunn, although I think that makes us much better in the short-term. If Walman develops, it may not even hurt us that much in the long run. But trading Dunn is a tough pill to swallow.
However, there are Pittsburgh fans willing to do Coyle+1st. Coyle is 26 and a 40-point player with 2 years until UFA. Someone even said Donskoi + 1st. He has a year left and has never hit 40. If those are the returns they want, trade for a guy like that and add to get Kessel in a 3 way deal. Or just add lots of extras to Berglund/Sobotka to make up for the slight age difference.
Blues get : Kessel
Ottawa gets: Tage Thompson + Blias
Pittsburgh gets: Dzingel/Pageu + WPG 1st + 2nd
I mean that would be the basic framework. There might need to be some small incentives to Ottawa, and Ottawa could be replaced with any other team looking to rebuild/shed salary. Kessel just checks far too many boxes not to go after him. RHS, PP specialist, fast, can offensively elevate a line without an elite C (Bonino). And if we shed enough salary and the cap rises, we can probably add Tavares too. We talked about Hoffman and Tavares, Kessel is les than $2M more. We slept on Kessel 3 years ago, and he sold for a pittance. Since then he has 2 cups and 275 points.