The reviews say that the Leica Monocrom has an extra stop of DR and noticeably better tonality than a mono-converted image, so presumably the same applies to the Pentax?
When I shoot mono, I just convert from colour in LR, but if I was a pure mono shooter, I'd consider a pure mono camera. Partly because of the apparently better tonality and DR, but also because psychologically it probably makes you "think in mono", in a way that you tend not to, when using a normal colour camera.
I actually admire Pentax in a way for sticking with DSLRs, just as I admire Leica for their rangefinder cameras, or Fujifilm for their retro-styled cameras (I also love old motorcycles, as much as modern superbikes). I think it's great that these old "formats" are kept alive, with their image quality and usability improved to modern standards.
So I say good luck to Pentax, and I think they have a good future, but they need to learn that if they are going to be a niche product, they also need to move more upmarket in terms of cosmetic finish (they look a bit to plasticky to me).