US spent a good deal of money to churn out Chinese copies of Soviet small arms and funnel them to Pakistan who then sent them over the border into Afghanistan to be used against the Soviets. Will look through the sourcing for this later.

Re: Present day: The dynamic that you hint at will not work well at all. For one, no matter what the Taliban says today, the Uighur issue is going to be an issue between the two of them. The Taliban does not need to be as deeply enmeshed with the TIP/ETIM as they were back in the early 2000s, the Chinese state is extremely paranoid and any facilitation of Uighur extremism whatsoever will not go over well whatsoever.

Then there is the India issue. Obviously Afghanistan is going to be used as a staging ground for extremists who will launch attacks in India. Obviously. The Indians know this and are going to eventually wake up to the fact that letting Pakistan/Taliban run these camps inside of Afghanistan is not going to be good for India... but the choices for India are slim. The ANA is very obviously not up to the task. The only real option is to facilitate lots of connections with the various local warlords and hope that the tide eventually turns against the Taliban, which doesn't seem like a very likely event.

Then there is the Pakistan issue. There is an article in the WSJ today which, if you take it even remotely at face value suggests that the Pakistanis are concerned that the Taliban will be emboldened after they take Kabul and will turn against their former hosts. Maybe. Pakistan is playing a very, very dangerous game regardless. They have already been burned by touching the hot stove repeatedly but so far the burns have been more minor. Maybe the stove will be even hotter when its flame isn't directed towards Kabul, so to speak.

A serious question is: If a Taliban offshoot, perhaps backed by elements of the Pakistani state were, 5-10 years down the line, making serious inroads against Islamabad, would China intervene militarily? Would the US?