Warrick is an expiring, the only reason he is in the deal is so the Suns can take on Johnson, and getting Johnson and especially the pick are the only reason the Suns are taking part. There is no way they would do the trade just for the pleasure of waiving Brad Miller.
And the Hornets cannot sign him and "dare the Suns to match" because unless they get rid of Miller they dont have the space to make the offer. And I am pretty damn sure that even if the Suns just felt like being kind, or have been drugged, that New Orleans does not have the flexibility to take on Johnson, Warrick and Lopez.