Well, I do get the "mirrorless thing". It's simple: with an ultracompact MILC like the A7 I get the world's best available FF sensor AND can go "really small and light" whenever I want to. With any Canon-DSLR ... I can't.
Yes, I want a FF MILC! NOT as a "special purpose second cam" in addition to my existing APS-C DSLR (7D plus assorted EF-S and EF/L lenses from 10mm [=16mm FOV eq.] to 200mm [320mm FOV eq.]) but as a total replacement. I am tired of bulky, noisy, mirror-slapping DSLRs laden with swinging mirrors and submirrors, detached phase-AF units, heavy viewfinder prisms, mechanical shutter units and other opto-mechanical components that need to be precisely manufactured, assembled and adjusted to 1/1000 of a millimetre just to get a sharp picture. I want to fully cash in on the "digital dividend". :-)
And to be as familiar as possible with my gear which I don't use every single day, I want to run one camera system only at any time. Not two or three different camera systems from differnet makers with different user interfaces and different sets of mutually incompatible lenses and accessories.
My idea of "pure photography" is: make it simple. Purely electronic and digital. No moving, mechanical parts inside. No obstructions in the lightpath, that need to be moved out of the way for every capture. No retro crap. Only the dials and buttons absolutely needed. And ... let me see the scene as closely to how the camera will capture it, not as closely to how my naked eye sees it - to get the latter, all I need to do is open my left eye. :-)
So here I am, ready for my first "100% digital" camera. Compact and light. With a 36x24mm sensor to have full DOF isolation potential and excellent Hi-ISO IQ [I need 3200 frequently, 6400 rarely, never more].
All that Canon [and Nikon] are offering to customers like me is inadequate and only maximizes THEIR profits at my expense. "BUY an APS-C DSLR, BUY another one that is only marginally better, and another one or BUY a FF-DSLR (5D III/D800) now, BUY a 5D IV (D900) in 2015 and maybe - but only maybe, BUY a Canon [or Nikon] FF MILC in 2017. Priced at USD 4000+ of course, since CaNikon "really really need some high margin products".
Unlike many others, I am not willing to go that route. I want to cut that short and am looking for "small, yet fully competent gear" now. Not in a rush, sicne my 7D is still fully functional, but sooner, so I can wait a little. If the Sony A7R is not there yet, maybe it's the A8R or some other product by somebody else. :-)
Also unlike many others, I do not need a "chunky camera to hoöld it steady and have a good grip". I'd prefer it to be small and light, when I want to go small and light. And unobtrusive for strreet photography and any other candid situiation. And for those weekend city trips we like to take. And all those nice photo walks with camera and buddies. And when I go mountaineering - I want it to be so small that camera + WA-pancake on it fit into a small pouch attached to my backpack strap up front, ready to take a shot whenever I want to . And for my urban exploration excursions in some industrial ruins, where I need to climb over fences or through broken windows. Large heavy gear is a pain! But inside it is fairly dark, so a small-sensor compact will not cut it. Or for Aunti Mary's 80th birthday party. Or for my niece's wedding. And when I go mountain biking in breathtaking alpine scenery. And and and.
I know, I cannot go small and light with any camera system, on occasions that demand use of fast/longer focal tele lenses. But in all of those situations listed above I hardly ever use my 70-200/2.8 II or even longer tele lenses. And when I occasionally use one, most of the time it will not be handheld but sit on my tripod. So using an adapter (with tripod ring) and handling bigger lens on a small camera body would be no real issue for me. As I am doing now, I'll just switch to liveview and (touch-) screen control. Maybe there will even be adapters offering full functionality of EF lenses not only for AF but also for in-lens IS. It's just a bit too early to make a call on this. Another "chunky" lens I would love to have is the Canon TS-E 24 II. No matter what cam, I'd always use it on a tripod. It doesn't have AF or IS on a Canon DSLR either. So no problem to use it via adapter on a MILC. No risk of a protruding viewfinder bump getting in the way of max. shift [yes a Nikon problem, not Canon]. :-)