thay are already way past 8 gpu cores in a computer, i mean what do you think super computers use to render insanely huge and i mean huge images?
the public will not need such graphics card for another 10 years or so, because we still want it to be a "PC" Portable Computer, the computers that use these graphics are nowhere near portable, they are the size of a good server room or two.
if its possible yes, do we need it now? no, will we need it in near future? very unlikely