I agree with jrista about EVF's been a long way away from being truly good, but I also agree with your point that technology grows quickly, and it certainly will get there, probably sooner than the decade that jrista predicts.One of my co-workers brought in an Olympus E-M5...we played comparison between it and a 7D. The EVF on it is comparable to the 7D, it takes better quality pictures in poor light, about the same in good light, and I really can't tell the difference in AF speed or accuracy. I was amazed that this camera was so good. It's hard to deny the existance of something you are holding in your hands... this wasn't just an EOS-M killer, it was a Rebel killer too, and if it wasn't for the way better user interface on the 7D and Canon Lglass, it would have topped the entire APS-C lineup.
And apparently Olympus has announced that the replacement for the E-5 will support both 4/3 and micro-4/3 lenses, which kind of implies that it will be micro-4/3 with an adapter. Nikon users are also complaining about there being no D400. My guess is that everybody is working on professional mirrorless cameras and that the 7D replacement will actually have the name "M1". When it comes is anybody's guess.
Something like the Metabones Speed Booster makes this possible.. That device has a magnification of 0.707 and gives a 1-stop improvement in maximum aperture. However, the Canon version of APS-C is 1.6X not 1.5X. Therefore, a Canon-specific booster could have a magnification of 0.629 and give a 1-1/3 improvement in maximum aperture.