Originally Posted by NickC 
Make a small high quality body to match the limited lenses. Two dials, Pentaprism, SR. As small or smaller than the original *istD.
That's my order!
Pentaprism + SR = no small body. I'm pretty sure that the current Pentax models are as small as they think they could make them, at least with current tech. If you want a small body, you're going to have to give something up. My guess is the SR (eg. Oly 520 vs. 420). I'm pretty sure that the pentaprism adds a lot to the size as well. There is no free lunch in design.