That would cost them a lot I'm afraid You basicly want 7D2 features in 60D/70D and 5D3 features in 6D.
Software features, yes, but the hardware (af array, fps, digic processing power, camera build, button layout, ...) is vastly different and leaves enough to be desired when buying a more expensive model.
Imho Canon goes over the top with this firmware crippling, it's not complete feature removal (like 60d afma) but cutting back features so they are nearly useless. For example they removed the option to save the source files for in-camera hdr from the 6d ... but you can now play audio tracks along your slideshow. Or the options for setting functions to keys is strangely limited, and they went out of their way to make the dof preview button nearly impossible to access.
I doubt a lot of people upgrade to the 5d3 because you can save your hdr source files, but I'd wager the guess that Canon manages to annoy a lot of 6d users or owners of other, lesser and cheaper camera bodies.