Nick - people that buy a 53MP (or 36MP) camera are definitely thinking about prints, not displaying on the web or computer screen, and are looking at large prints, i.e starting at 16 x 20 or larger. They are also thinking about a wider gamut than sRGB.
Target audience would be wedding, fashion, fine art, portrait and landscape photographers. This type of camera would be competing with the medium format lines.
Don't forget, upsampling means loss of detail.