@Jrista - you shoot with a 7D. You've shown that you can take good pictures with it. I get your frustration with Canon's release schedule. Who knows the exact reason. But as a complete solution, if you can get better elsewhere then you would have moved. Is a 70D sensor really that bad? Based on it's target market, I think the MK II will do well. Even with a tweaked 70D sensor.
I do shoot with a 7D. I also shoot with a 5D III. However...generally, nearly all of my work is shot at high ISO. At high ISO, the differences between any camera on the market with similar sensor sizes is trivial. The full frame definitely does better...not surprising, it gathers more total light for any given identically frames subject. The 7D suffers at really high ISO, it does pretty well between ISO 400 and 1600, and there have been times when It's done quite well at ISO 3200. The 5D III does excellent up through ISO 12800.
Jrista - Most of your pictures are taken at high iso, where there is no problem. For Astro work, ok, clearly Canon is way behind there. Where you feel you need the extra DR/low noise is on landscapes on those occasions where you shoot awkward scenes (ie range greater than 11 stops), and you don't/can't use filters or HDR?
If those extra 2 stops and the greater latitude that you can get from Nikon are critical for you, and all other things balance themselves out, then you have your answer...
But, people have been taking amazing shots for decades, and printing them large, without problems. I get the fact of your frustration. I get the fact that sometimes when you have to lift shadows there is more work than would be with a Nikon or Sony. But, how many of your pictures which are up to selling
1) Are ruined because of the Canon sensor limitations?
2) Are noticeable by your average purchaser?
I think we all strive for perfection, getting the picture as much correct in the camera rather than post. But when you boil it down, how much of a problem is the Canon sensors (bar the Astro point which is well made)? Each and everyone of us has a different threshold. And whether we complain because wifi should be included, or whether we want a 100-400mm MK II or indeed a better sensor (i for one would love to get ISO 12 and ISO 25 which I used to get in film), it's good to provide the feedback for Canon, it's good to sometimes vent out our frustration.
But it's also good to put it in context - both from our perspective, and Canon. They're out to get best shareholder return. We're out to make the best pictures possible. Nothing holds us to each other - if we don't like it, then we can move. If we're a Pro, then we factor that into our business case to move. If we're amateurs, then I think the average one only has a couple of lenses and can move easily. Those with 4 or 5, not as easy, but still possible.
In my "photographic lifetime", the biggest impact to my photography has been having the time do it, and traveling to some amazing places - that's been the biggest improvement. Practice. Technically, live view, the 1D series of AF and the L lenses have improved my shots, the 1Ds MK III allowed me to take some great shots, but so did the 5D. Everyone's mileage is different...