I'm quite familiar with Olympus history and have owned several Pen, Pen Fs as well as OM, E-system, IS-system, and Pen digital cameras.
Look at the photo you presented. The Pen F SLR is mostly empty space inside, room for the mirror to move, the film cartridge and film to move, etc. The Pen digital, if you ever open one up, has virtually no space to spare at all.
EVFs are not huge but they do take up some space. Using the Olympus VF-2 as a guide, they'd need another 1.5 cubic inches of interior space to put it in. Never mind the advanced IBIS system that fills most of what looks like an SLR prism hump on the E-M5. A quality optical viewfinder will not be any smaller either.
So you could build a Pen with an internal EVF or OVF, sure, but it's going to be larger than the E-P2 at the very least. Rearranging the guts of the Pen E-P2 can be done, to some degree, but the body MUST grow by some amount or you are giving up space in some other components to do it. Where exactly to put the EVF and keep the Pen F like look is a tricky business.
I had the flat-top Panasonic L1 DSLR, which had a similar sidewinder mirror optical system to the Pen F SLRs (and shared some parts with the Olympus E-330 model). Believe me, it was about double the volume of the E-P2—a much, much bigger camera. I love the shape and ergonomics, but the reflex viewfinder was perhaps its most challenged bit.
I'd like it if they made a Pen digital that was just like the Panasonic LC1 in design:
But note that this camera, with a fixed lens and a sensor a quarter the size of the E-P2, is larger in virtually all dimensions. And it doesn't have IBIS either.
I'd still love it. ;-)
G
I beg to differ.
If you are familiar with Olympus history, you'd know that Pen series are not the same as the OM series.
The Pen digital cameras are the digital successor to the Olympus Pen half-frame family... which *has* a built in viewfinder.
It's pure bunk to say that because it has a flat top therefore there's no place for a viewfinder. Olympus had done digital cameras with that model exactly (E-300 and E-330) and that's back a decade ago.
But I admit that most people may not realize this distinction (I am an Olympus nut), and may blur the OM-D with Fuji X series. So your point is valid in this sense.