The logical fallacy at the centre of a lot of this argument from the mirrorless size tends to be....
Mirrorless performance may one day equal DSLR performance = Everyone wants a small camera
The idea that mirrorless tech could be used for anything but size saving seems to have passed many people by.
What I think you need to consider as well is which format sizes are actually going to benefit more from a smaller flange distance. In this reguard ASPC seems much more obvious than FF to me, the overall smaller size of the lenses is the most obvious point but your also dealing with a format where DSLR's use a legacy flange distance that's longer than needed for ASPC mirrors and a smaller sensor that causes fewer problems with light angles.
I look at the FE lens lineup and to me its notable how long they look relative to similar DSLR designs, I'm guessing the product of having to correct light angles. In seems to me that you could effectively just be trading shorter flange distance for longer lenses.
* angle of incident light (short flange distanze, lage sensor) - yes it is a problem. Yes, it can be solved, as Leica has demonstrated. Can it be solved for 10mm less flange distance, at far lower cost (than Leica) and still giving excellent image quality - I believe(!) yes, and I believe (!) it will be proven soon enough
* Once Mirrorless cameras will finally be "really right", i.e. "solid state" with no moving parts whatsoever inside [=no mechanical, but global electronic shutter] will have a LOT of advantages over (D)SLRs beyond bulk and weight. Here are the ones I am interested in:
- 100% vibration-free operation = benefits to image quality, especially "when it counts" = in challenging capture situations
- 100% silent operation possible = ability to get any images or the images you really want in many capture situations e.g. concerts, churches, theaters, candids
- flash X-sync down to 1/8000s ... or whatever shortest exposure time will be = images possible, that are currently totally unthinkable
- higher image quality - no misalignment of optical axis and sensor/focus plane possible - provided lens mount is solid and precise
- lmore bang for the buck - significantly fewer parts, no moving parts = significantly lower cost to makers, due to easier assembly, precision-alignment, quality control = lower prices for cameras possible (!)
- higher reliability = no more mechanical defects possible, only electronic issues = significantly less failure in use, significantly shorter repair-turnarounds ... just swap out a circuit board, finished. No re-alignment of components required
- much faster cameras possible ... fps as high as we want them possible - only limited by procssing power and bandwidth - and those follow Moore's law, so we'll have plenty, very soon :-)
- better information at time of image capture - thanks to EVFs - which will continue to fast-evolve from "just acceptable in early 2014" to "absolutely mind-boggling" in the near future
And I am sure, we are still missing a few. :-)
* Relative lens size
does NOT scale 1:1 linear with sensor format! Not on SLRs. Not on MILCs.
Yes, 1" < mFT < APS-C < FF lenses. But with "really right" designs, the difference is rather small (ceteris paribus).
And beyond approx. 135mm physical focal length there is NO difference, since only the size of the entry pupil dictates size of the lens at the the end of the day. As evidenced by existing tele-lenses (mFT, FT, APS-C) and by the fact, that longer tele-lenses are not made for smaller than 135 ("FF") image circle.
That's why I expect some APS-C mirrorless systems to be around for a few more years, until everything gives way to FF. Anybody "really into" photography - whether professionally or as an enthusist/amateur - will get FF MILCs [sized very compact or as large and heavy as a current pro-DSLR for those who prefer "large and heavy"], everybody else only interested in "snapping a few" will use their mobile devices ... which will get better and better IQ in extremely small form factors [think Google glass :-)]. The middle-ground will disappear. But again, thats only my expectation, no fact (yet). :-)