I think obviously the bolded is still key. If you're going to move Kassian, it's gotta be for the right price. It's gotta factor in what he could become.
That said...as it pertains to playing with the Twins, i still don't really think that's the best fit. I think anyone can have a stretch of productive play there, but i don't think it really plays to his strengths in what he could be as a player, just being a big net-front lug with the Twins, and i don't think he's really an ideal puck-retriever for them either.
I don't think "all out" Kassian is really the same sort of player that i'd expect say...Virtanen to become either. But there's a big difference between "totally engaged and hustling" Kassian, and "floating and trying to play a pure skill game" Kassian, who just simply doesn't seem skilled enough to get by on that.
Those brief stretches we've seen where he seems to strike a balance on that, those are awfully encouraging...but they're also so few and far between overall. Also the reason i think you might be able to sell him "high" relative to what he's done so far in his career. Though if you can't...obviously there's no point really.
This idea of waiting on him to "break out" for good though, has to have some end to it. At some point, either he becomes a legitimate top-6 scoring forward with size and the whole shebang, or he doesn't...and you've got yourself a defensively weak bottom-6 banger who doesn't often go "all out"...with the odd flashes of scoring touch. Which is an okay play to have i guess...but i think you'd regret not "selling high" on him if that's where it ends up. Especially when you throw in the back issues which are already starting to factor in...it's just one of those conditions that often haunts guys for the rest of their careers. Certainly if that becomes a chronic issue with his back, it's going to be a lot tougher for him to consistently play the way we all want to see him play. The whole point of Kassian really, being that he can be big and physical and "rugged" as a scoring winger...potentially. If the physicality and ruggedness gets removed from the equation...he's not a very "unique" player anymore.