If you've got a franchise player and you're talking trades with the Celts, I think you ask for Smart, Crowder/Bradley, Brown, and both Nets picks, as a starting point. You don't agree to do a trade unless you get three of those pieces, with the 2017 Nets pick as a deal-breaker.
If you're the Celts ... do you risk trading that 2017 pick? I don't think you can. Even adding Jimmy Butler might not put this team over the top of Cleveland, let alone Golden State.
But getting a top two pick in this draft might set the team up with a blueprint for being competitive and fun to watch for the next decade plus. Very few teams get the chance to have a win-now core featuring multiple All-Star talents and also put together a core for the future by picking in the top 10 in 4 out of 5 drafts.