Wow so Kim Jong Il is finally caving in? Wonder if his son had anything to do with it.
My impression is that Kim has been talking about some kind of economic zone for some time now. So I am not sure he's actually doing it.
About possible tactics. I don't think China wants NK to have nukes. First of all, it's always wise not to share any secret weapons with anyone. Allies can become enemies in no time. No matter how close China is with any of its potential allies, China only wants itself to have nukes if it has any choice. There is no reason for China to want NK to have nukes. Secondly, letting NK have nukes would push SK and Japan to start their nuke programs, which is definitely not what China wants. Plus, having a potentially unstable neighbor with nukes is also not a good thing. So no matter what, China does not want NK to have nukes.
IMHO, one thing China can do now is to bite its time and wait 'til the old Kim goes away, which won't be long. His son should be a lot easier to manipulate. I'm sure China would bride some NK officials close to the young Kim so that Kim can become some kind of a puppet. One huge weakness of the hereditary system that NK (or ancient China and other parts of the world) is that later generations of a powerful leaders are usually spoiled and become weaker and weaker both politically and character-wise. This happens to every dynasty in China's ancient history and in the West as well. I'm sure the same trend would hold in NK.
or China could start a coup and put a China-friendly Kim in the throne. I think China has the capability to pull it off.