Are me eyes deceiving me? The left nozzle looks squarish whilst the right nozzle looks more "roundish". If true, then there might a hint of 2DTVC of sorts; or testing of two different engine configurations (the latter being highly unlikely). Or just a case of some flaps at top of left engine...A rear view photo of J-XDS, posted by Cute Orca on Weibo with the caption "If this is not a PS-ed photo, this shows that the J-XDS has full-moving wingtips and no angled vertical stabilizers."
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Also, whilst not definitive, the belly did not appear to show the deep trough / channel in the light grey prototype