The "64 megapixel question" is this:
how good can the MTF be at about 50lp/mm and distances of up to 14mm from the center of the frame be for (a) current good Canon 35mm format lenses, and ( future professional level EF-S lenses, if and when Canon makes any such.
My guess: if Canon chooses to do it, they will be able to make lenses that can handle the job.
By the way, I read recently of an analogy between some DSLR developments and what Oskar Barnack did almost a century ago: creating a new high quality camera in a far smaller format than ever before, exploting the increasing resolution of the light sensitive media available, and relying on designing new smaller format lenses of distinctly higher resolution. That was the essence of the Leica revolution.