Well, what did it take to bring another young former-ROY point guard Jason Kidd to Phoenix 12 years ago? Apparently, all it took was Finley and Cassell. But, unlike the Hornets and Paul, Dallas wasn't winning and Kidd wasn't happy there. So to answer your question, it would take the Hornets to miss playoffs next year and Paul to start demanding a trade. Not very likely.
Paul would have to become a RFA and decide not to want to play with the Hornets anymore (see Joe Johnson). Then the Suns would have to offer their franchise in a sign and trade. In other words forget about getting Paul, at least until he becomes much older. Maybe the Suns can get him for a year or two right before he retires.
My guess is that there are at least 100 quality players the Suns could get easier than Paul.
Right now there is a real premium being placed on top point guards. Without him, the Hornets are just an OK team trying to get into the playoffs and he's still on a rookie contract. No one trades players like that.