John – I used the iPhone example for impact; and you are right, other than to prove a point, I can’t think of any pros or serious amateurs who would use one, because of its limitations.
As a design engineer, you above all, should know that there is no “one size fits all” solution for cameras (or anything else). Design parameters ultimately drive performance. Just as I don’t use the same shoes on the shop floor (the ones with steel toe caps) as I would when I am out hiking (full-height hiking boots), the same analogy goes for cameras. A full-frame DSLR is something I will use most of my work, except when weight and size become an issue; then I will switch to something smaller and lighter, fully understanding that this will limit the way I photograph things.
As for the E-M5 (and I reserve the same comment for the Nikon Df), building a camera that uses a body shape that takes us back to the film days, really makes little sense photographically. The medium (film) and the production technologies (casting and metal stampings) drove those designs. If manufacturer’s have to revert to the “retro look”, rather than technical innovation to move cameras, there is something fundamentally wrong here. Design decisions should be made based on ergonomic / human factor considerations and manufacturing capabilities. Skeuomorphism is out of fashion; would somebody please inform Olympus and Nikon.