I dont know why people are sour on OJ Mayo. Kids got 4 years NBA experience and he is only 24 years old. He hasn't been given a great role in Memphis but has still done a great job as a 6th man. His reduction in minutes has hurt him in figuring out his role and he has only shot 40 - 41% in 26 minutes over the past two years but has still averaged 12 points a game...
However, in his first two seasons he started all but one game, and played 38 minutes a game in year one as a rookie he averaged 18.5 a game with 4 rebounds shooting 44% and 38% from three, in year two he averaged 17.5 a game while shooting 46% and 38% from three. All while playing sufficient (not great) defense, but running well and hitting down shots and getting to the free throw line.
Putting a young experienced athlete alongside Rondo would benefit the team, and the celtics organization would greatly benefit Mayo. I think he would be a steal for us honestly. I would trade the 21st and either this years second or a future second for him.