Good point on the 120mm. Many of the OIS lenses will have a element that appears to move when the lens is powered off. I have both the 50-140 and 100-400 and the 50-140 has the same issue. Also if the GFX glass is like all the other X OIS, most will make a slight noise when the lens is on the camera and the camera on, even with OIS off. The 50-140 I have is by far the loudest in this regard. Outdoors you will not hear it, but indoors for sure. I have tried a couple of other 50-140 lenses from other photographers, and they all make a bit of noise, but not as loud as mine. Mine was early in the life. As the 120mm is only lens with OIS, if you hear a rattle in the 63 or 32-64, something may be wrong.
One note, Fuji will continue to add features functions both via firmware (so existing cameras can take advantage of them) and physical changes. A classic example of this is the 4 way button on the X-T1. Early cameras you really had to push hard to make the buttons engage, and there was a lot written on ways to add material to the buttons. Later cameras Fuji fixed this with a different version of the 4 way that had a much more tactical feel. The X-T2 had the better style buttons from the 1st ship.
But Kudo's to Fuji for all the extras that they passed on to the X-T1 in the 1st year with firmware, like ES and improved video.