I've already disposed of my 5D. My Pentax K5 offers all the quality I need in a very compact package. My G3 I'm testing appears to do the job to in an even smaller package.
For the sake of argument, I can conceive of one way that advances at a given format size like the D800 could hurt a smaller format like APS-C, in defiance of the persistent trend towards smaller formats "getting the job done", and that is that an even smaller format encroaches from the other side, and we move back to the traditional scheme where the sequence of formats went mainly by a doubling of linear dimensions: using the short edge (also film roll width), 24mm, 42.5mm=1 3/4", 100mm=4”, 8". That could leave a format like the 13mm on the short edge of 4/3 format as a natural next size down from 35mm format and strand APS-C.
I do not see this happening with DSLR's, where both "incumbency" and lens sharability with 35mm format favor APS-C formats, but maybe with mirrorless systems, where there is far less priority on backward compatability with "big old 20th century style SLR lenses". Especially if Canon follows Olympus, Panasonic, Nikon, and one half of Pentax in going smaller than APS-C for a mirrorless system.
By the way, my subject line throws in the high end compact format 2/3" because that happens to continue my size halving sequence. As a hostoric quirk, that was the format of the first Olympus DSLR, the fixed lens E-10.