I don't think CP3 will go to Miami because they have roughly all of their cap space absorbed by Wade/Bosh/LeBron. There is no way getting around that, and I don't see a max level player like Paul taking the MLE and giving up roughly $70M (or 2/3 of his value over 5 years) just to join that group.
That said this trade would have to come with an agreement on an extension. You don't trade Rondo, and his team friendly contract, for one year of a better player at the same position. That would make no sense beyond this year.