I guess it'll take Canon aps-c at least another 5 years to get to 5d3 level, but I'm certain they'll get there eventually - the limitations of aps-c are lens resolution and pixel density, I don't see why there would be physical any constraints to low light capability.
If Canon were to release a new APS-C camera with 10MP but 5D3 low light performance would anybody buy it?
7D is niche, and rebel target market get sold on silly things like numbers.
What about an APS-C camera with 6 or 8MP with 1DX low light performance?
don't really need anything more than 6MP if I'm being honest, and I'm sure most
of the APS-C market are the same...
Canon reduced the resolution of their premium compacts a while back and have reduced the resolution of their flagship model... all for IQ dividend.
Apart from the benefits in pixel size, the vast majority of EF lenses would better fit with the lower resolution sensors and have more usable aperture range too.
Folk may salivate at the D800, I don't, I wanna go 'backwards'!