There was a time where I would have LOVED to get Butler... But now I'm not feeling it.
After seeing Minnesota enter the "Butler sweepstakes" and discussions about #5+LaVine or even #5+Wiggins for Butler... I think it's fair to say the Bulls will ask for a king's ransom for Butler. (And it should be noted even the TWolves are very hesitant to trade #5+LaVine alone for Butler now, and the Bulls want more as well)
And the Bulls deservedly so should ask for a king's ransom for Butler, but the Celtics in that case should keep #3, Bradley and the other fillers they may have had to trade (like Rozier, #16 and Jerebko). Don't blow up the core for a guy who scores just 5 ppg more than Bradley and has defense that might be slightly inferior to Bradley (no offense to Butler).
It's also hard for me to include Bradley or Crowder in any deal because I love those guys, but the Bulls definitely want them as a starting point in any deal so I say no. There's a reason lots of teams like Chicago want Bradley in a deal. They love him, All NBA First Defense, bargain 3 and D guy (valuable in today's NBA), and he has already received praise about his defense and hustle by other players (like IT, Lillard, etc.).
Crowder gives Lebron fits and his perimeter defense with Bradley is lethal in the league (makes it a lot harder for opponents).
And hey, Bradley is an "All-NBA First Defender" that can also score 15-16 PPG. Bradley and Crowder are a big reason why we are actually competitive against Golden State everytime we play them.
And lastly, Durant isn't coming here this year even if we trade for Butler and/or sign Horford this offseason. Our best bet is to ask Durant this offseason what we could do in the next two free agency periods, the 2017 Draft and trade deadline to convince him to come here, while he does a 1+1 in OKC and tries again for a Final with the Thunder for another season before he, Westbrook, and Ibaka all enter FA.
So yeah, I think I'm in the "Don't trade for Butler" sweepstakes now. Just draft someone like Brown, Murray or Dunn (I'll be happy with anyone honestly I'll trust Ainge for now) and don't blow up the core this offseason.