I do not see him in the NBA this year, never mind the Celtics. I think they already have a bonus built into his contract to get $50,000 after he is cut, so long as he signs with Maine and plays with them in the G League next year. If anything, that is his future for this next season, getting lots of playing time in the G League.
If you want Tacko to have a future in Boston, I think this is best for that. He wouldn't be getting any run whatsoever on the team, so best for his development to be playing somewhere next year. This way he can do that but still be under the influence of the Celtics without the Celtics having to add to the salary or take up a roster spot. Besides, way too many young players/rookies will be on already, don't need another.