I believe the goal in trading for Butler is to pair him with Crowder. I have mentioned this before but if the Cs can land Butler (who may or may not be at odds with Hoiberg) for Smart, Picks and any other player other than IT, AB or Crowder then the Cs are on a championship path. For the sake of speculation lets say the Cs trade Nets pick #3-#5, Mavs pick #16, Smart and a future 1st.
In my opinion the key to that roster would be Ab moving to 6th man. I think the addition of Butler would put the Cs out in front for Horford. Even if a FA big man is not added and the Cs just resign Sully and retain Amir the key will be their small ball lineup.
IT, AB , Butler Crowder and a big man is an elite small ball group. With Sully at the 5 they are ECF contenders add Horford and you are a championship team.