The original 645D was a category killer camera that won awards and all kinds of acclaim, but still received very little interest in the general market. There were all kinds of reasons for this -- the price, the general perceived lack of lenses, lack of major marketing by the company outside of Japan, people being satisfied with their 35mm kit or being dissatisfied but held back by some of the shortcomings of the 645D.
The plan around the 645Z launch, plus the camera itself, are addressing several of the key challenges faced by the 645D. The launch price is ~20% less, the performance of the camera is much improved with some key "creature comforts" from current 35mm kit such as Live View, and the FA lens series is being officially brought back to North America. Even tethering support might be better. Other challenges remain, one of the biggest being that this is still a particular camera that isn't designed for everyone. So even if the market interest in the Z is 10X the level of interest in the D, it still will be a relatively niche product... though I predict it will be a successful niche product.
Anyway, I'm not overly worried about the current level of interest out there, as long as it's enough for Ricoh to keep supporting this platform for a while yet. Because this is a camera that was designed for me.
I built out a pretty good kit with the 645D and I'm going to get hold of a 645Z as fast as I can. If it proves out, I'm going to be very pleased with it since I'm already very pleased after 3+ years of hard shooting on the 645D, even including blowing a shutter after 50K actuations on one of my bodies.
I have just recently decided to put an end to nearly my entire Canon 35mm kit because I really dislike using it any more after shooting the 645D system. I had just as much, if not more, invested in my Canon equipment so I will take that loss when selling everything off. Even though several Canon lenses will be painful to lose, I've found the 645 lenses more than good enough for most of what I do, as is the rest of the 645D system. The things it didn't do well were (mostly) not really critical for me. There are some exceptions, such as Canon's tilt-shift lenses. I'll retain those and pair them with a new Sony a7R and a couple of Sony FE mount lenses. That will be my lightweight travel rig and my architecture kit. For everything else where it can be used, the Pentax will continue to be #1 for me.
So far in my 3+ years of travels with the 645D, I've only encountered one other 645D shooter in the wild. But already in the past few weeks I've met two new ones locally who jumped on board with 645D purchases once the 645Z announcement hit and the D prices came down. A few more photographers will come into the 645 digital system that way, not just all with net new purchases of the Z. Many D owners are potential Z owners, sometime later.
I'm not rich, and I don't think I'm crazy.
What I do is make photos in which I love details, tones and colours; and I like to print, whether small or big. I was convinced by the first files I saw come out of my 645D in Nov. 2010. If there are more photographers like me out there, then the 645Z can't fail to do much better than the 645D. Especially if the image results really deliver on the promise of the tech specs. I intend to find out soon...