I can only speak for myself, but after having had an original Canon Digital Rebel for a decade, I was in the market for a new camera. I am not a pro, but a serious amateur that has sold a few photos in local summer festivals. I have not gone beyond 8" x 12" in size, so my 6MP rebel has been good enough for all these years. After renting a number of cameras, I decided on a 6D because of the potential to do large prints (up to 30" wide) for the place I work. Some things that I liked about it compared to my original rebel were the electronic level and the ability to save some custom settings. What I didn't like about it was the size and weight, the lesser zoom and lesser DOF than my crop sensor camera. But it is great for landscapes!
One of the cameras that I had rented was the new mirror-less Olympus EM-5, I liked the smaller size (especially when paired with the reasonably small 75-300mm zoom, 150-600mm equivalent). It also had a electronic level that could be always on - a definite advantage over the 6D's level. It also has the ability to save 4 custom menu settings and lots of other nice features and settings, including in-camera IS. While I didn't ultimately buy the EM-5, when the EM-1 came out, I bought that along with the 75-300mm zoom and their 14-54mm four thirds lens.
I saw that Canon now has the always-on electronic level on the 70d, but I didn't think that was reason enough to purchase that camera as I was looking for something smaller and lighter than the 6D for my other camera. I looked at the SL-1, but as others have mentioned, Canon just won't put it's more advanced features into their lower end cameras. So, no electronic level or saved custom settings (as far as I can remember). Plus, a definite negative when it comes to Canon, in my opinion, is the lack of mid-level lenses. You seem to have basically cheaper kit lenses or extremely expensive L's. Those lenses are becoming even more expensive as Canon adds IS to their lens line-up. With the Olympus, I have in-camera IS and the lenses are comparatively cheaper because of that.
In terms of IQ, when I rented the various cameras, there was little to differentiate them at the print sizes I am likely to use - aside from the FF 6D, which clearly had the advantage. The smaller sensor Olympus cameras - at least in my opinion - were the equal of the Canon crop sensors cameras. The Olympus lenses I have are not their highest pro-level, but their mid-level lenses, but, so far, the 14-54mm lens seem as good (if not better) than the Canon 24-105mm L. To buy a zoom lens longer than 300mm for Canon will break the bank and be far heavier than I would want. The small Olympus 75-300mm (150-600mm) has no real equivalent in Canon's world.
I have no idea how successful mirror-less cameras will be and how they will affect Canon and Nikon, and I really don't care too much as long as Canon and Olympus stay in business! But, for me, Olympus mirror-less proved to be a better alternative than the current lineup of Canon crop-sensor DSLRs.