Trading the only All-Star talent on the roster, plus the only asset currently likely to yield an All-Star talent, to get a single All-Star caliber player ...
Doesn't really seem to get the team much closer to where everybody wants them to be, does it?
If the Celts trade for Butler, they have to avoid giving up their current core players (Thomas, Crowder), and they should also avoid giving up more than one of the Brooklyn picks.
Otherwise, I don't think the trade will do enough to move the team toward contention.