incorrect, it is much easier to scale up UAV because you dont need as many pilots. as well, long endurance flights are taxing on pilots, UAV eliminates this problem.The efficiency gains from going unmanned diminish as the size of the aircraft increases. For an aircraft as large as GJ-X, the gains are probably fairly marginal. Size also correlates with cost, and as such GJ-X is unlikely to be considered an expendable asset. There must, therefore, be other compelling reasons to eliminate humans from the cockpit, sufficient to outweigh the downsides of doing so. A requirement for very long duration, high-persistence missions is one possible answer: an unmanned aircraft does not need to sleep.
American B-2s have been involved in a number of missions with flight times of >36hrs, up to during the initial operations against Afghanistan. However, these very lengthy missions required multiple in-flight refuelings from (unthreatened) tankers operating from (unthreatened) airfields scattered around the globe, something that clearly does not apply to China's strategic context. It therefore seems unlikely that the limits of human endurance are the reason for GJ-X being unmanned.
So here's a thought: could it be a tanker?
the idea of it being a tanker is quite plausible, making it a multi-purpose platform like H-6 to HU-6.