As Mattster has pointed out, China has indirectly supported these terrorists for a long time. So, I am not sure how trustworthy this 'call of Al Queda against China' is. It could just be a bogey
EDIT:
Having said that, if Al Queda is honestly wanting to go after China now, then it is bad news for China. Firstly, all that Al Queda has to do is use some disgruntled group of Uligars to mount a dramatic and violent attack on of the cities of China. China would then be under pressure to retaliate, at the same time it wont be able to retaliate on the sources of jihad. Because
#1) They have themselves nurtured them and helped Pakistan nurture them.
#2) They are not present in Afghanistan, and NATO will not allow them in Afghanistan(atleast not right now).
That will leave China only one option: To retaliate against Ulighurs. China may or may not do it. And either way, it will help the terrorists' agenda.
If China does not do anything but to bolster its defences, then the terrorists will be emboldened and will plan more audacious attacks. For Eg: India knows there are talibani fighters trying to enter India, yet India does nothing except tighten the defences, India does not punish the talibani fighters or their instigaters and hence the terrorists get emboldened.
If China reacts and bites the bait, by going after Ulighurs, then more young Ulighurs would sympathise with terrorists and Al Queda. This will again prove counter-productive. Though in the long run, this approach may work better but it would be bloody and costly.
Also, if an attack happens in China, then China will have concentrate on terrorists, and use its resources to strengthen its defences against them and fight them. Both are taxing on economy. China does not have this problem compared to nations like US, UK or India. Also a big attack, can scare of future investors.
Once US was attacked on 9/11, it triggered a series of events which have leeched the US' economy. This could also happen with China.
But one significant advantage that China enjoys, that no other country has is that, Pakistan is totally under the grip of Chinese. Even US cant effect the kind of emotion, that China can. So China will use their greater power within Pakistan to neutralize the terrorist ambitions towards China by either goading the Islamabad to go after those groups that are against China, or by directly dealing with terrorists and arriving at a settlement(political or financial) or directly entering Pakistan with its troops after due 'permission' from Islamabad. This is an advantage that US has not had in its War On Terror. US never had a sincere Pakistan by its side. In the final analysis, that could be very critical element. Pakistan has from the begining of WOT, has only been begging for aid and more aid without any tangible action on ground. The things may be different if China was in the position of US.