I'm sure nVidia considered it, but I believe that VIAs X86 licences is nontransferable and would be voided if another company bought them. So the only way to merge nVidia and VIA is to have VIA buy nVidia, and well, fat chance of that
Well, they can't, it's part of the deal with the x86.
VIA and Nvidia should work together. Not combine, but Nvidia should make chipsets for VIA, that kinda stuff.