Exactly what pentax is doing and is a big shift for MFD. Inversely, I sold the majority of my 35mm kit and I'm loving MFD. I would probably drop my 5d3 to an aps-c camera if I was in a pinch but I wouldn't let my Blad go so easily.
The problem Pentax seems to have is that it really doesn't have the resources that Canon or Nikon would in terms of either offering improved features or building a modern lens line-up.
The 645z has more AF points that most MF cameras for example but there all clustered around the centre because its reusing an ASPC AF system, really not much better than your typical central AF point on other MF cameras. As you've said before it lacks LS lenses as well.
With the lens selection on offer today the 645z to me clearly seems to be aimed at the landscape/macro photographer. The problem I'd say is that whilst the body is much cheaper than alternative MF the lenses are not and these markets are very price dependant, there aren't many amateur or pro landscape shooters who can afford to spend $15,000+ on their setup.