The old (circa 2014) Sony IMX161 sensor is seriously holding everything else back. Per people's comment: "it looks like a XE-1 and focuses like one", while other, smaller and newer Fuji cameras are attaining blazing speed. It is very likely that the all-new GFX100S, being loaded with the fresh from the oven IMX461, will outperform its smaller brethren. An odd sight it would be though.
Still, the next generation could be nice. It would be quite feasible to see a successor in 2022 that boasts 2018 smaller-format performance. Into that I would buy...