Thanks again for the replies everyone. They were genuinely helpful, both in terms of concrete feedback on solutions and also general validation and perspective.
I've had a few more days to play with the K10D and the KP side by side. I think the comparison is giving me a more objective picture of the KP. Now that I can focus on some specific points, a few revisions/clarifications are needed.
1. I withdraw my comments about the KP meter wake-up time being materially different. Once the meter goes to sleep (no more overlay visible in viewfinder), it might be that the KP takes 200ms while the K10D takes 100ms to wake. But I can only really perceive that by adjusting the controls and observing the time it takes for the viewfinder overlay to appear. But the real functional duration of time it takes from mashing the shutter button to actuation is basically the same, especially if you factor in AF time.
2. As a corollary of 1, the shutter speed and aperture settings are visible on the LCD even when the meter/overlay goes to sleep. In Av the aperture updated in realtime on the LCD, just like a shoulder display. Being able to toggle the LCD on using the function dial is great.
3. The startup time of the KP is definitely slow in comparison. Turning it off when looking to fire off shots on the go is not a good idea. It needs to hang out in standby. How that compares to the battery life of the K10D in an equivalent shooting scenario, where I can turn the camera off, I don't yet know. Theoretically, sleep with meter off should be very low power.
4. Additional time with the cameras has really highlighted some ergonomic differences. The KP is really hard to shoot single-handed with big hands, unless you're comfortable with a finger position and grip force you'd only otherwise use for a 5.12 grade climb. I removed the L grip and replaced it with the S and it feels way better, less sharp angles. However, I need to depend on my palm and second hand to really stabilize it. With a tele like the 18-135 the weight is so far forward that two hands are necessary. It sucks that there is only a bit of soft grip on the left side-front to grab with my left hand, versus the nice curved edge on the K10D.*
I really wish companies published their product manager's design brief with their products, because it would be illuminating. The big LCD is clearly the center of the design here. It dominates the back of the camera, starting with a massive bezel all the way to the left edge. It stretches across the camera to the far right, where it leaves little room for the condensed button pad and even less for the vestigial rear grip.
This use of space comes down to two things. One is that the LCD itself is bigger than the K10D LCD. The second, more important factor, is that it is articulating, which necessitates a robust bezel. A fixed LCD could get away with small bezels.
Why does it have such an LCD? Certainly it allows for a somewhat improved review experience, given the size and ability to review results from a fixed and pre-configured shooting position below eye-level. It also supports live view shooting, which is obviously the point here. If I had to envision a design goal that summarizes the KP for me, it is offering the benefits of a mirrorless camera in the smallest DSLR form factor possible. No need to live view and you basically don't need an articulating LCD, which wins back a lot of camera real estate. In my limited experience, I've found the live view slower than my Lumix LX10 compact camera at focusing, and the lack of touch screen to be a significant drawback in the LCD-centric workflow.
On the right shoulder one finds two additional dials, one used for controlling various functions (AE, HDR, etc) and the other for controlling the settings of those functions, or for controlling exposure settings when a special function is not engaged. On the top front, instead of a horizontal dial like on the K10D you find an equivalent larger vertical dial (parallel to surface of the camera).
These additional dials exclude the possibility of a shoulder LCD in the design, and the front dial in particular is positioned in a way that prevents the existence of a larger grip (or, conversely, allows a thinner grip).
Despite all these changes that could make the camera more compact, the center thickness behind the lens mount is about the same as the K10D, so the thinness seems theoretical at best, and messes with the weight balance of the camera. A forward, thick grip offers an inherent balance point in-hand against the weight of the camera body and lens combined.
I guess what I am realizing now, is that the KP probably exists because some photographers really do like live view for static subjects in good light. Studios, landscape, architecture, etc. Additionally, it is a technological bridge forward for Pentax in evolving the use of the LCD as part of the shooting experience (versus merely the review of results).
I am not yet convinced that is what I need. I like the K10D for its simplicity, directness, and clarity of purpose, I just wish it had a better sensor.
But I don't see a good alternative to the KP right now in the Pentax world. A K3 looks closest to the K10D in terms of size and ergonomics, and if that is what I had bought, I wouldn't be posting here right now. But I feel it's too much of a downgrade in terms of AF and low light performance to rationalize a downgrade. I got a new camera for new camera performance. A K1 is way too much.
So I guess that puts me in line with the rest of everyone looking for a K3 successor. The KP is not that, it is a different kind of camera. I wish I had understood that beforehand, but I nonetheless look forward to exploring its capabilities and adapting. Change is always hard and technical innovation often looks like waste and inconvenience at first...
