Boston would have to do it. Conley is a lesser pG, but a much better shooter, which helps with spacing, and the C's have some premier sharers at SF with Pierce and KG at PF/C. Horford's above average too. And the upgrade from current frontcourt to KG/Horford is tremendous. Horford is 26 with consistently 18+ PER and good defense. If this trade were to occur, we'd have Horford, Conley, Sully, Melo, Lee and Green signed for the '15-'16 seasons for about 41.3 million, plus whatever for Bradley. Dumping Lee/Green sometime in between and signing Bradley reasonably would likely allow for a Conley/Bradley/??/Sully/Horford w/ Melo roster plus room for a max type contract.
(this is why signing a guy for 4 yrs 36 million just because "we were over the cap anyway" in year 1 of the deal is terrible logic, btw).