I'm gonna agree with others who cited cameras like the Canonet and other fixed-lens non-zoom cameras as evidence that the x100 series is and always will be relevant. It's a simple recipe that has always worked for a certain kind of photographer. And it is always going to relevant, and in demand.
I'm also gonna agree with others who said that a full frame X100 variant makes no sense - the additional power requirements, cost, and questionable gains in IQ coming from a future FF X100 model vs. an APS-C X100 just don't stack up. Anyone who wanted a fixed focal length 35mm P&S could have spent almost 3x more on an RX1 II - and without actually checking sales, I'm gonna assume based on the seat of my pants estimations that the x100 (in all it's S/T/F variants) have outsold the RX1/R I/II family. And price was likely a big part of the reason for that, although form factor and UI may have also played a part. At this point in the development of their X platform, I'd guess that sharing the same XTRANS sensors throughout their family of cameras is part of what keeps the x100 series affordable.
I would like to chime in here and add one of my own personal "wants" for the Fuji X family in general - I would LOVE to see Fuji back away from the megapixel war a bit and develop a lower resolution (say 12-16MP) APS-C XTRANS sensor optimized for all out ISO performance rather than just more pixels. While I love my X-Pro 2 and X-T2, I'd gladly have traded a few pixels (16MP on the previous gen XTRANS was fine for my needs) for better outright ISO performance. And even faster AF would be nice too of course - from what I've read on Fujirumors and other news sources, it would seem like one of the biggest bottlenecks in AF performance is currently the X100's 23mm lens, which may simply not be able to focus much faster than it already can.