Being unrealistic:
Lebron forces a trade to Boston for Lee, JJ, Young, Rozier, and all of our first round picks.
PG: Smart, IT
SG: Bradley, Turner
SF: Lebron, Crowder
PF:Sully, KO
C:AJ, Zeller
I'm not sure that team can win it all against the West, but it's definitely coming out of the East and considered a contender. With that defensive pressure and the literal fact that every single guy in that depth chart other than Zeller (who spreads the floor in his own right) can hit the 3, that would be a team that nobody would want to see in the playoffs.
More realistically:
Melo forces a trade to Boston for Lee, JJ, Young, Rozier, and 3 1st round picks.
We convince KD to sign with us after we take Cleveland to 7 in the Eastern Conference Finals, giving us a 2016 roster of:
PG: Smart, IT
SG: Bradley, Hunter
SF: KD, Crowder
PF: Melo, KO
C: AJ, Zeller
I think that team is a front-runner for the title. The scoring and shooting is ridiculous, and Melo is much more effective both offensively and defensively as a PF than a SF. We'd still need to eventually upgrade the five position, but playing small-ball with that lineup certainly isn't going to really hurt us in today's NBA.