As you point out, the only people who have to wait are brand loyalists. Obviously some people have to be, but those who don't might as well do what some of us have done and supplement our Canon bodies with an A7r. I love mine, both with its superb native primes and my Canon EF lenses (plus a few old manual focus lenses) - so much so that I'm not sure which is my second camera....
I'm not necessarily a brand loyalist but the economic reality is that I have invested in Canon and to change to a completely incompatible brand now isn't feasible for me. I have looked closely at the A7r for that reason but there seem to be three big question marks - light leak, AF performance and IQ when using an EF adaptor. You clearly love your A7r but what is your experience with these issues if you don't mind me asking?
I don't mind at all.
1. It's not a "completely incompatible" system; they overlap. Whether they overlap enough for your purposes I can't say, of course. I would also say that for many people a complete switch to Sony wouldn't be sensible or desirable, and that I have no intention of doing so. For me it's a marvelous adjunct which, in some situations, would be my go-to camera - at least until Canon comes up with a close substitute (high resolution, mirrorless, no loss of EF performance, etc. - preferably with IBIS...).
2. The light leak applies under very limited circumstances, apparently (very long exposures in near-total darkness but with a bright light hitting part of the lens mount), and doesn't only apply to Sony cameras. Check out Roger Cicala's blog post on the subject at lensrentals. I never shoot in such conditions, so it's simply not an issue for me (or, I suspect, for 99.9% of people 99.9% of the time). The shutter-shock problem is far more real (see below).
3. AF performance with EF lenses is unquestionably inferior in terms of speed - it's not *that* slow, but if you're used to the near-instantaneous focusing you get with the best Canon lens/body combinations it will seem slow (rather comical too - it ambles towards the subject, pauses, goes a bit beyond and then comes back); and it's slow compared to native FE lenses, of course. But it's probably not inferior in terms of accuracy; in some respects it's superior: one benefit of a mirrorless body is that with on-sensor focusing there's no need to worry about back/front focusing. If you plan to use it to photograph things that don't move, it's not an issue. But don't even consider it if you want to photograph sports, children running around, herons-catching-fish, etc. and rely on AF to do so.
4. As for IQ, I've used these EF lenses: 24-105L, 28mm 2.8 IS, 40mm, 85mm 1.8, 100 L (no AF with this, but the other electronic connections work) and 70-200 f4 IS. I haven't performed anything resembling a scientific comparison of these lenses on the A7R vs 5DIII or 6D, but I feel confident in saying that not only is the image quality not inferior on the Sony body it's probably superior (I was shocked by the superb image quality I was able to get from the 85mm 1.8 when I first attached it).
At the time I decided to buy an A7R I had used one exclusively with Canon lenses - it was because the results were so good that I wanted one, and it was not until I had owned it for a while that I bought the two native FE primes; they're superb too, especially the remarkable 55mm 1.8.
Having said all that, there may well be Canon lenses that don't work as well on the two Sony A7s - I have no first hand knowledge one way or another - but based on what I've read the main problems are with wide angle Leica lenses due to a design that simply doesn't apply to Canon lenses. I would also add that if you want to use old Canon MF lenses, it's far easier to manually focus on a mirrorless camera (thanks to magnification and focus peaking) than it is on any dslr, especially if you use wide apertures; and Sony's focus peaking and magnification work at least as well as anyone else's.
5. One flaw you didn't mention is the much-discussed shutter-shock. This is real, and, in my experience, shows up if your shutter speed is 1/100-1/125, regardless of the lens (apparently it's worse if you use a tripod, but I don't and thus can't comment). It doesn't seem to be a problem at other speeds, including slower speeds (though you may encounter the usual too-slow-shutter problems if you're not using a lens with IS; IS has no effect on shutter-shock, of course); I've taken plenty of sharp photos at 1/60 (a speed these cameras seem inordinately fond of if you let them decide the shutter speed). If you avoid 1/100-1/125 you'll be fine.
I hope some of this helps. Far more competent/savvy/knowledgeable people than I have written about all of this, though, so don't rely too much on what I've written!