I've replaced GB3466WQSU-B1 (which I managed to damage successfully with my studio monitor) with GB3467WQSU-B1 and indeed the flickering issue has clearly been addressed by iiyama. Not only that, but there are some other small noticeable improvements I wish were implemented with the older 3466 model. For instance a separate power button, no external "socket" around vesa mount so thi time it was much easier to hang the monitor on my desk arm mount, the OSD display information is now continuously refreshed so I can quickly see changes in current Hz rate, white text on black background no longer turns yellow. I'm almost glad I smashed the older model!
EDIT: I've recalibrated the monitor and with a more faithful sRGB colour representation I'm more than pleased with it.