Beside those 2 reasons It could be to increase the robustness of the system in case the supporting infrastructure is down. You still have alternatives, It is all speculative
Do you mean the "kill chain" needed for the targeting or some other support infrastructure ?
I don't quite understand how using a plane would help if the "kill chain" is down - considering the range of the ballistic missile you would still need information from other sensors and if you could get this information to the H-6K in the air you should also be able to get the information to your normal missile batteries.
Perhaps the PLAAF just wants to get in the "ballistic missile game" and not leave it completely to the rocket force ?