IT, Butler, Durant, Amir, Horford. That's a contender.
Also impossible cap wise. It would have to be something like: IT/Smart, Bradley, Butler, Durant, Horford
That is practically as impossible cap-wise. To get Horford and Durant, the Celtics need to waive Amir and Jerebko, and probably find a taker for James Young. Then to acquire Butler, the Celtics need to either move an additional $13.5 million in salaries if traded after KD and Horford were to sign, or $18.5 million beforehand. If they traded for Butler in August, a month after signing the #3 pick, it could be Crowder, Smart, and #3, or Crowder, Rozier, Hunter/Mickey, and #3, but those are really steep prices to pay. I personally don't see what's wrong with IT, Bradley, Crowder, Durant, and Horford as a lineup, with an actual bench.