Interesting discussion, let my add my $0.02 of thoughts.
The top end mirrorless market is now pretty much the domain of Sony and Fujifilm. The Four Thirds competition has folded up their tents and left. Even the mighty Samsung, with huge resources from consumer goods and cellphone sales, gave up in disgust. They could have kept their NX line as a loss making poster child, but chose not to.
The current Canon EOS M mirrorless lineup isn't quite good enough for the Sony and Fujifilm crowd. Nikon seems to be years behind, but they will release something really profound. Real soon now. One of these days. Promise.
Where does all this leave Pentax? A proper mirrorless will need a new lens mount, which will soak up R&D funds that could go towards new K mount full frame lenses. If they do release such a thing, the fan boys (that's us) will ask for a K mount adapter. Not just a mechanical adapter, mind you. It is already possible to put a K mount lens on just about every mirrorless body ever made, with manual aperture and focus.
An official Pentax adapter will have to do auto focus and exposure. The fan boys (that's us) will want an adapter with a built-in motor for screw drive autofocus lenses as well. It can probably done, but will soak more of those precious R&D funds. And this miraculous piece of technology will have to be competitively priced, as well.
Pentax already tried the mirrorless K-mount thing with the K01 and it didn't work out well. It was a bit of an odd duck in the looks department. Autofocus was not quite up to the standard set by its mirrored brothers. With only a rear screen, it had the same limitations as phone cameras. Perhaps if it had an EVF, things would have been better, but that would have made it even more odd. A DSLR sized body with an empty mirror box, who wants that?
In any case, a full featured mirrorless isn't much smaller or lighter than a DSLR. I just compared my NX1 to my K-x and there isn't much difference. The Samsung body is slightly thinner from front to back and that is about it. Width, height and mass is very similar.
One can use a DSLR as a mirrorless - just press the live view button. That isn't always going to work, though. In the end it comes down to whether an OVF or an EVF works best for you. After decades of OVF use, an EVF is slightly strange. I don't use the EVF on my NX1 very much. That lovely rear screen works very well.
The EVF has the edge in one important niche - manual focus for those who wear prescription eye glasses. You are looking at an image on a screen. No additional lenses in the optical path from front lens element to eyeball to introduce focus errors!
I'm not holding my breath for a new Pentax mirrorless. If it does appear, I might be in the market for one. For now, the NX1 scratches my mirrorless itch very well.