Thanks Peekayoh. That's the type of technical response I was looking for. In other words, more would be demanded design-wise from a wide angle lens on a mirror less camera if the size were to be kept down. I suppose that makes it advantageous to use other lenses with spacers when shooting wide angle.

Electronic viewfinders are placed where your conventional optical viewfinders are.
Overpriced? Sony Alpha 7R - $2300.

Full frame lenses made for mirror less cameras are much small because they don't have to compensate for the extra distance between the back element and the sensor plane. Compare some of the Sony A7 lenses to same focal length/aperture full frame Canon and Nikons.

Here is an article listing some of the shortcomings according to one reviewer. I have not been able to find one in my area, so I have no first hand experience.

http://photo.stackexchange.com/questions/34193/disadvantages-of-electronic-viewfinders

For those who are already invested in 35mm type DSLRs, moving to newer mirror less interchangeable lens digital cameras from their chosen brand will be a relatively easy transition because they will be able to use their existing lenses. Those of us looking to enter the mirror less field without a DSLR collection of older lenses will be forced to buy older lenses and use adapters or make do with the limited offering of built-from-scratch lenses made especially for mirror less cameras.

Nikon and Canon have a considerable collection of glass for their existing mirrored DSLRs. I don't think it's as easy as putting old lens elements into a shorter barrel because the back focusing characteristics will most like require total redesigning. I'm not an optics expert, but the transition to mirror less could be slow and expensive for manufacturers.

Oldtigger asks "Why redesign lenses?"
Look at the size difference between full frame lenses for mirrorless cameras and their equivalent for DSLR.
Adapting a 35mm film lens to a mirrorless camera defeats the purpose of having a smaller, lighter body.
The process of going from legacy 35mm cameras to unfettered digital cameras reminds me of evolving from "horseless carriages" to the "automobile".

Interchangeable mirrorless cameras have a couple of obvious advantages over DSLRs. Less bulk due to the absence of the pentaprism and mirror, and smaller lenses for the same focal length and aperture. There are problems still with electronic view finder speed, but that's still new technology and will likely improve.
My question concerns whether lenses for mirrorless cameras will be easier (if not cheaper) to design and manufacture to the high standards required by hi-res cameras.
I'm not sure how many of the legacy SLR film lenses are actually up to resolving 20+ megapixel sensors, so starting from square one with the new mirrorless format should be a good thing. So far, the only full frame mirror less camera (Sony Alpha 7) has few dedicated lenses available, and everything Nikon and Canon offer for their full frame DSLRs is hung over from the 35mm film days.
Any other thoughts on the development of mirrorless interchangeable cameras would be appreciated.

I used to have a Program called Painter from a company called Fractal Design which later sold it to Metacreations which sold it to Corel. The latest version is a handful, but there are Lite versions now for both Mac and Windows at $50.

You don't need to subscribe to a cloud version of Lightroom. You can buy it outright for around $135.

There is another list called "Aperture Vs Lightroom" which is winding down (for obvious reasons), but the owner is putting together a transition guide for Aperture users facing the switch to Lightroom.

Try here:
http://aperturevslightroom.com/how-to-migrate-from-aperture-to-lightroom/