I have never hit the frame number full problem on the X-T1. Page 123 of the handbook says the shutter will lock after 999_9999, and that the solution is to format the memory card, set Frame No to Renew, take a photo to reset it to 100_0001, and then change Frame No back to Continuous. So although it is irritating, especially if you have photos on the card you cannot backup and which you do not want to delete by formatting, the solution is simple and seems to be easier than on the X100T.
As an experiment, I have just carried out that procedure on my X-T1, and the frame count was indeed reset to 100_0001.
Page 332 of the X-T2 handbook contains similar instructions.
To prevent this problem arising, once the folder number gets near 999, it would be a good idea to carry out the reset as described above at a convenient time rather than wait until the shutter locks up.
I have some way to go before I reach this issue.