Francesco Sisci writing in the Asian Times says that recent Chinese maneuvers aimed at force projection could be a wink to NATO and the US that China is prepared to assist in Afghanistan. Sisci goes a long way to showing why China would be useful to the NATO powers in Afghanistan (which, aside from the Byzantine possibility of settling some kind of grand deal with India and Pakistan, has plenty of obvious benefits for an international force that is pleading for more troops).
Galrahn of Information Dissemination believes it to be wishful thinking. (He does add that it would be an amazing thing for Obama is he managed to convince China to participate.)
I would like to put forward my thoughts on a possible hook to bring China into Afghanistan, which unfortunately is part of the possible problem with doing so.
Xinjiang. The Taliban was not only allowing anti-US radicals to operate bases on its territory; it is well known that there were Uyghur nationalist (and possibly terrorist) training bases as well. If Afghanistan was to collapse again, it will happen again. In particular, the East Turkestan Liberation Organization and the (possibly non-existent) East Turkestan Islamic Movement are considered allied to the Taliban.
Unfortunately, the price for getting Chinese help would probably be a free hand to do as they like in dealing with these bases and "terrorists". And, for all the faults of the US in the handling of the War on Terror (and I would argue there are quite a few), it is difficult to believe the Chinese would be less brutal than we have been. Moreover, China would most likely demand an independent structure, due to their strong feelings of sovereignty. (It should be noted that while China contributes to peace-keeping, it has never provided peace-keeping TROOPS, but only engineers, police, doctors, etc.)
I'm not willing to say which would be worse, the complete disintegration of the Afghan government or allowing China the kind of free hand they would likely want in Afghanistan. But dismissing the idea as fantasy doesn't help, and neither does thinking it would be cost-free.