I'd be surprised if the Celts trade KO, just because I think his value to them as a shooter who can adequately defend both big positions is enough that he probably isn't worth trading unless it's a lottery pick or a two-way starter coming back the other way.
It's hard to see another team giving up that kind of value, unless there are other assets involved.
Well, I guess it depends upon what you think his ceiling is. If you think he's pretty much who he is, then I think the much cheaper JJ can provide pretty much the same amount of shooting from the big position as KO, with much more defensive versatility. JJ doesn't provide the playmaking and passing that KO does, but that's not needed nearly as much with Horford there, who is one of the best playmakers from the big position.
Further, keeping JJ next year will come at a price around Crowder's salary or a bit more; whereas, it wouldn't surprise me to see KO get more than Turner this summer.
Would you trade him straight up for Noel, or even adding a later first round pick (like Boston's 2018 pick)? Though I'm still not convinced that Philly would even want a big back in return, even with KO's offensive versatility. Perhaps if it was expanded a bit to be KO and Rozier for something like Noel and Covington, that would make more sense.