I think the elephant in the room is capitalizing on the DPE. To me, the ideal trade partner would be Dallas for BOTH of Dirk and Nerlens Noel. As much as Cuban might resist at first, his business mind will supercede, and realize that with these players, Dallas is still a bottom feeder.
The Celtics can offer something like one of Marcus Morris/Rozier/Smart, plus a combination of Boston 1st round picks (end of the draft) and 2nd rounders
Ideally the player we see go is Morris, who is hurt. It allows Dallas to truly tank, and get assets for a guy like Dirk, who likely wants to play for a title, Noel who would be very useful as a PF/C in any of Brads lineups. Beefs up our frontcourt and our overall bench depth, but also gives Brad a varoety of starting front court options. Dirk comes off the bench in the regular season and then starts come playoff time for one final sprint for a title.
Dirk can then do the Paul Pierce thing, and sign a one day deal with the Mavs to retire in Dallas.
If Noel pans out, we can work a long-term deal. Either way, his value increases substantially getting meaningful minutes for a playoff team.