X-Trans and Video never were good friends.
Both, the X-TransI and X-TransII sensor had some serious issue with moiré in videos. However, already the X-Pro2 dramatically improved the Video Quality of Fuji Cameras.
But what about the 4K on the Fujifilm X-T2? Videographer Emmanuel Pampuri says:
Picture quality is amazing. […] It’s more cinematographic than the GH4 […] We don’t have the f-log on firmware right now, Fuji is still working on it. […] Picture quality is very sharp. There is no aliasing, no moiré… it’s beautiful. […] I can use it properly 100% for the Video […] Fuji is still developing the firmware. I get a new firmware every two days […] Battery life is not so good if you don’t use it with vertical grip […] It’s still a CMOS sensor, so there is still an issue with the rolling shutter.