actually, if retina type displays come onto the market from other companies (which they will) or even 4k monitors then using 3 x 4k monitors would be Ahem... 25894080 Pixels rendered per frame
at least 30FPS.. means = 776822400 Pixels per second
so yea.. given textures, larger tessellation models, multi monitor, larger resolutions etc... i can see this. Also what about cloud game streaming perhaps companies are clamouring to sell huge VRAM cards so that millions of players don't need scuppered textures?
and finally remember, these boutique cards can come with bells and whistles they still get sold to the rich / e-peen crowd. Further more even scientific / military institutions might use huge VRAM for modelling 360 degree simulators and insane resolution too, that's a few sales right there.
its not all about crysis 2 and skyrim @ 1080p