Pentax just announced an unusual mirrorless body, the K-01. It continues to use the venerable K-mount, but that also means the mount is still far away from the sensor, to accommodate a swinging mirror that is, ahem, no longer present. What follows is camera-nerdy, and is mainly just a prediction I want to get on record.
Compared to its mirrorless adversaries, the resulting body is thick. Imaging Resource published a preview that has side-by-side pictures of the K-01 against some other cameras, and you can see how much thicker than a small micro-4/3 body this one is. (The Sony NEX was curiously absent from the comparisons, but it's about as thick as a micro-4/3, albeit using lenses that are closer in size to typical dSLR systems, including, ahem, the Pentax K-mount).
I didn't really get the idea of taking a dSLR and whacking off the mirror box until Pentax made a second announcement this week. They're bringing out a bunch of new lenses soon, but this post has a big picture of the most interesting lens right at the top: a future lens for the K-01, where half the guts are going to stick inside the camera body.
That very flat lens will not fit on a conventional Pentax K-mount body: there are bits of lens well behind the lens mount, and the mirror would get in the way on any conventional body.
I think this is the first of many of these special lenses, and they'll let Pentax advertise something very interesting: a K-01 body will be a bit of a chunky camera, but a K-01 with special "XS" lenses will be one of the slimmest system cameras around! Even better, Pentax uniquely has a library of very flat lenses to draw on. The first announced XS lens was a 40mm f/2.8, which was an impressively super-flat update to a lens they have made for about 40 years (it also will work on normal Pentax SLRs, as it happens). Just looking at this new XS lens, I speculate it's a variation on their 21mm f/3.2 pancake, with everything pushed further back into the body (and resized to be APS-C only).
Pentax has one other pancake in its portfolio, a 70 mm, and I expect it to be the next lens in the XS series. All three of these lenses are very unusual: to my knowledge, only the micro 4/3s system has mainstream pancake lens options. They're notably lacking from the current E-mount options for the Sony NEX series.
The core selling point of the K-01 camera will then be: yes, you can use every piece of K-mount glass ever made, when you need to, and the camera will be big. But when you want a small, carry-around camera, you can put an XS lens on it, and the camera, despite its body thickness, will be more compact than any other APS-C camera, and competitive with the micro 4/3s models. Buy all three of the XS pancakes, and you can have a wide, normal, and tele lens set that fit in a small pocket.
I don't know if the K-01 will be a market success, but I think it is an idea that physically makes a LOT more sense than you would think at first glance.