Morning
As there are so many types of photographers it's only possible to offer a personal opinion and I in no way consider this to be the general view but to me, the Pentax makes little sense. I agree somewhat with synn's comments, I don't see a one camera fits all situation as being possible, different systems excel in different areas and whilst there are some excellent generalists, there are none I believe that can do everything perfectly.
That said, I'm not really sure what was missing from traditional ccd based mf systems, they excel at what they were designed to do, i.e low iso's, resolution, colour etc. and if you're a commercial studio photographer like BC et al. then the newer tech would apparently offer little benefit. The Pentax obviously has great high ISO performance but looking at numerous files, the difference between high end 35mm and good glass is minimal to my eye so rather than the slight bump in resolution, I don't see the benefit of paying the extra for the Pentax, particularly if lenses are either questionable at the cheaper end or expensive at the higher end. As a landscape photographer, I see little benefit over 35mm and zeiss wides for example, certainly not enough to warrant the cost, I doubt there would be much cost difference between say a D810, zeiss 21 and otus 55 against a 645z and a 55mm. Now weather sealing is a benefit but maybe I'm lucky, I have used my cameras everywhere from +50c in deserts in Iraq to -45c in Antarctica and never once had an issue caused by environmental issues, that's not to say others haven't just my personal experience.
Live view is obviously a plus for some people but having looked through many mf viewfinders, I've never felt that I couldn't focus accurately, live view on a tech cam, fantastic but not possible with the Pentax so again, I'm struggling to see the benefit.
It feels a little as though the newer cmos mf systems are bridging the gap between 35mm and traditional ccd mf backs but do they really need to? It's almost like they are solving a problem that doesn't really exist. There will always be people who want this camera and good for them, I hope they enjoy it but for my personal uses, it just doesn't seem to offer enough to compete with ccd mf or high end 35mm, it just sort of floats in the middle.
Anyway, just my opinion, if it evolves in to a system where it will flash sync at higher speeds, has great quality and reasonably priced lenses that allow the sensor to sing, will tether reliably (I appreciate that is on the way) and will offer real image quality improvements to the current 35mm offerings then I will look again, for now though, I will just enjoy shots others take with it. As an aside, I absolutely love Nicks shot of the trees, stunning because he captured it, I don't really feel that it couldn't have been captured equally well with a 35mm system that is smaller and cheaper.
Have a nice day!
Mat