The K-1 is a great size for ergonomics when handling. Small for FF but large enough. It's on a strap or in a bag it feels large in moments when doing something other that photographing. I do the neckstrap hand wrap thing when out and about because it doesn't fall right when cross chest strapping. The annoying thing is that your hand is then fixed to the camera cyborg cannon style making it useless.
A K-1 with the K-3III depth profile would be amazing. It's the depth that makes the k-1 a bit awkward, sometimes it feels like a spherical camera
A more potruding viewfinder would also be more comfortable. I feel like prying that whole rubber rim thing that holsds the screen off the camera
edit: One reason it feels awkward is that I tend to opt for smaller prime lenses. People shooting zooms will have an unwieldy camera anyway. When I mount my rather large and heavy samyang 24 the size and balance of the camera gets so messed up anyway the camera makes very little difference.