Not to beat a dead horse, but hey, just remembered so I will anyway...
I actually
have experience with what it would be like using the K-01 with a big heavy lens on the front for an extended period of time. It's in reference to this outing / event...
Furthur - m8ofoto's Photos
...And that's with a lens less than a 1/2 the weight of what I was referring to in the OP...
The first few dozen photos were taken with the viewfinder and my modified grip shown in the OP. I wasn't getting the best hitrate on my focus. Many of those photos didn't make it to the gallery; some I left in as they had a certain 'artistic quality' added by the otherwise missed focus.
So I switched to using Liveview, and focus hitrate went-up by an order of magnitude. So after the first few dozen images in that gallery they were mostly taken in a manner the K-01 will
mandate photos be taken; by holding the camera up and away from my eyes, and holding the lens & camera up with outstretched arms. And I'll tell you, holding the camera+lens up (Sigma 70-200/2.8 HSM) away from my head was
definitely getting old by the end of the concert. Good thing I'm a sizable relatively strong guy. But considering a 300/2.8 + TC (1.4x or 2x) is about twice the weight of that ... I probably wouldn't have lasted. As a matter of fact by photo 129, I switched out the long zoom and put the FA 50/1.4 on instead, both to get wider angle photos and to give my shoulders and biceps a break.
...so yes, I'll agree the K-01 will
definitely mandate tripod / monopod usage with a big lens attached if one needs to spend an appreciable amount of time taking pictures. But my issue was/is this is not alway going to be possible or desired given the circumstances. There's what I mentioned in my OP and follow-ups as a circumstance when it's not desired. And here's another case, but where it's not possible. I'm not permitted for example to walk-in with my monopod to a festival as the monopod essentially has a spear on the end of it if you take the removable rubber foot off it; so one has to use their camera + long lens freehand. Now lift-up a 6 - 12 lb weight one or more feet away from your eyes, hold it there perfectly still for 10 - 30 seconds, and do it 100 - 300 times.