I doubt nVidia will be competing against x86 but rather x86-64, which has many of the "legacy" features you're no doubt thinking of (e.g. segment registers) removed or sequestered.
I wonder what ARM has to say about 64-bit computing, though
Bad news on that one, at least for the first generation of nVidia chips based on the Cortex-A15. Segmented address spaces? They're baa-aack!
I remember that back when the 64-bit UNIX was introduced in, IIRC, SGI machines. Nobody made a big deal of it. SGIs were already very impressive and nobody cared that much for the extra bits in registers.
I cannot remember when was the last time a single program wanted more than 4GB (I can, actually, it was Firefox and I left it running with a page full of Flash thingies for the weekend - by Monday, it was unresponsive and I had to xkill it). I can agree we need 64-bit addresses for servers (and we have been needing them for quite some time now) but not for desktops and certainly not for my own computers.