While Chicago isn't looking to move him, they apparently would with a "good" offer since they are concerned about keeping him long term and they would like to push for the playoffs.
I think Markkanen would be a great fit here as the long term 4 that the team could really use.
Not sure what a "good" offer to Chicago means, but would something like this work.
Smart, Pritchard, 21 1st for Markkanen, Valentine, Arcidiacono (Boston cuts Green or finds a team to take him or Edwards)
That seems like reasonable value for Markkanen. Boston obviously has to be willing to keep him, but that is the type of trade that at least makes sense long term in my mind. I'd do something similar for Collins/Snell from Atlanta as well, but I think I like Markkanen a bit more than Collins as he is a much more prolific shooter.