You are assuming that the NBA allows the Celtics to steal from the Hornets. They won't. CP3, even with the balky knee, is a lot better player than Rondo. You would have to throw in a bunch more stuff, and on top of that, convince CP3 that he should sign an extention here. For that to happen, they have to guarantee him that Howard is coming, and they will be able to sign KG, and Ray to another contract.
That is a lot of ducks to line up.
As much as it would be huge for the C's, all of that is not likely happening.