I recently attended a photography show in Toronto and hung out with the people at the Pentax booth (they even recognized me from the previous show!). In conversation with some of the reps there, they mentioned to me a couple of things about the FF future (and did hint about it coming).
When you think about Pentax and some of it's key selling points. They mentioned that small size, tough and rugged body were both integral design aspects of a possible new FF camera. They have invested heavily in APS-C because image quality is advancing steadily in this format. It also supports their small size and rugged body KSPs.
Once Pentax feels that they have developed a FF camera that is small enough with a good body it will be released at the appropriate time. IBIS may be part of the solution to solving this puzzle, but it wasn't expressely said that it was a main issue. Pentax really talked up the portability of the camera, so I think above all this is the bottle neck, so to speak.
p.s. Here's a picture of me with the new 560mm lens! I was asking about it's design, and again, weight was an important factor in it's design according to the reps. It is very light for such a long focal length, and much of that has to do with the design in comparison to other types of telephoto lenses. When asked, the Canadian MSRP will be "around $7000".
I got to handle the K-5IIs and the focusing is faster than the K-5 from my unscientific testing. It feels closer to 5dMKII focus speeds than regular K-5 speeds. Low light focusing seemed very accurate as well. Unfortunately, I wasn't able to save any shots on a memory card to take home as both models tried were pre-production.
I also handled the new 645 lens and it's quite a tank. Asked to try some photos with the lens as well. I could handle and try the lens, but no files allowed either.
Oh, and here's a K5 pentaprism! No mirror boxes here
sorry about the 'instagrammed' quality