Luffy doesn't seem to view PK as anything other than the culmination of his adventures at sea. There's no question in my mind that when all is said and done, assuming we don't have a tear-jerker ending, the moment he becomes PK, he'll immediateky go off to become the next great XXXXX.
I'm on the fence about agreeing with this. It's more like Luffy wants to be Pirate King to make a statement to others as well about the importance of exploration and adventure to me. And I have a feeling he'd probably either stick with it as the King and protect his crew and brethren much like Whitebeard does with the New World, or he'd retire immediately to let others try and take it and learn what it means to be the King of Piracy.