The datalink is one of the most sensitive parts of any warplane. I do not see either the Chinese or the Americans/Euros trusting each other enough to allow the other to have access to their own datalink systems never mind the kind of close co-ordination needed to make the two data links standards work with each other.
As such, you cannot simply add another channel to an existing AWACS workstation, you probably need another workstation altogether. On an aircraft with very restricted space and weight, that is not a viable solution. It is also likely that both sides would see even such an arrangement as being too dangerous.
For a ground based solution, space and weight become less of an issue, and you have even have the two sets of datalink operators on different bases if you want.
More the most ideal solution, but the only other alternative I can see to make everything datalink with everything else is if Pakistan developed their own datalinks and had them retro-fitted to all aircraft. But I think that may be beyond Pakistan's technological and financial capabilities for now.
As for not choosing the KJ200, well, maybe the KJ200 was just a little too much like the erieye for the PAF's liking. If you need to get two kinds of AWACS, at least you can try and get some difference in function.
Without the need for a rotating array, the radar can be bigger and longer ranged on a balance beam design like the erieye and KJ200. That comes at the cost of 360 situational awareness.
Therefore, having both balance beams and rotating dish AWACS can complement each other so you at least get some additional benefit out of the duplication in assets.
Also, I find it interesting the the PAF has opted for half and half between erieye and ZDKs, since the PAF is going to have far more JF17s and maybe J10s than F16s. It could just be the lowest number the PAF could cut the erieye numbers due to contractual rehasons, or the PAF may intend to buy more Chinese AWACS in the future as their JF17 fleet grows. But there is also the possibility that the PaF intends to use the erieye and ZDK in different ways and in different places.
With a potentially bigger radar and greater detection range, the erieye may well be better at early warning along a single facing boarder. With 360 radar coverage and probably more workstations, the ZDK would be better suited as an in-theatre command node, and also where the IAF might be able to easily strike from multiple directions at once, so Pakistan's coastal boarder with India would be a good example.
