Apple is 4+ weeks on back order of 5S. Will launching China Mobile now result in any more sales? Doubt it.
Let's bring on China Mobile when the manufacturing is at full holiday ramp but the Western holiday is over. I say bring them on during Chinese Mew Year and keep those assembly lines rocking for 3 more months. Why waste the announcement when you can't provide the product?
Besides, showing that Apple isn't desperate for China Mobile provides strength during negotiations.