My take away: Technology marches on. Physics not so much.
The headroom that is available for technological improvements is getting ever closer to the ceiling set by physics. So, from a practical standpoint, we may see some slight improvements in ISO performance from the next generation of 7D, but it won't match the performance of the last APS-H sensor Canon made.
Now, let me back up and say that we should all acknowledge just how good all the modern sensors are. If you can't take a great picture with any Canon or Nikon DSLR it is due to your own shortcomings, not the camera's.
It should be stipulated that this discussion, like almost all on this forum, is dealing with the margins. Small differences that won't affect most of us under most conditions. That's important because every once and awhile someone will assert that this or that camera or sensor is worthless. It's also important because we may refer to a particular camera as a "sports" camera, a "low-light" camera, a "high resolution" camera etc. etc., but that merely describes one characteristic of the camera and should not imply that it in any way limits its usability for other applications.
I started this thread because of curiosity about the upper limits of what could be expected out of a new 7DII sensor. We won't know the specifics until something is announced, but frankly, knowing what the limits are should help us set reasonable expectations and provide a basis for informed speculation about what such a camera might look like – until, of course, we actually see one announced.
Since I am now a 5DIII owner, I suppose I should not care. But I do. I still have a tremendous fondness for the 7D, but more importantly, I can still see it as a very useful option. I know my own financial limits and I seriously doubt those limits will allow me to own any Canon beyond 400mm. I may purchase the Tamron 600mm zoom, but no $4,000 lenses are in my future.
Also, not likely to be going on any $10,000 safaris pretty much assures me that I am likely to be distance limited under most circumstances. So, the reach of a good APS-C sensor inside of an excellent 7DII body with great autofocus, etc., etc., has its appeal.
...but I think you might be overlooking an important consideration for market differentiation-- video. That could surely influence sensor strategy as well.
You are correct. This has been a very "stills-centric" discussion and one of the unknowns is just how much emphasis Canon will place on video in the 7DII. That could totally upset the speculative apple cart.