The problem is, you can't merely retrofit refuelling systems on a plane like you would with an AESA radar due to the complex piping issues, unless the aircraft design was future-proofed to begin with. Or maybe they'll have a more finalized variant with such things like what was seen with the KJ-500 prototype.
The degree of complexity it would be for an aircraft to be back fitted with a refuelling probe would obviously depend on what if any prior arrangements already existed internally.
However even if such arrangements were not made originally I think upgrade packages could be developed for say the Y-9 and Y-20 family of aircraft with the requisite plumbing.