well it is in a way, the cores an updated 9800/r350, more advanced, more pipes, the advantege of it being fairly closely related to the r300/350 cores was driver dev was easyer and the cards could more easly share drivers.
ati updated the ps2.0b to version f, added more pipes, better memory controler, the list goes on and on, but it is an evolution and a theme/design.
just as the 6/7/8 are all evolutions of the same core, just a tweak here and there and higher clocks/more or less pipes/shaders thie x1k are a new design, modular by design, ati/amd could make a new version of the x1900 core that had 32 pipes and 128 shaders if they wanted (imagins that and drools) or 256shaders, because they can add/remove shaders pretty easly, just imagin if amd/ati are smart, they make a pci-e 1x card thats not even a video card, using the x1k design, 4-8 pipes, and a HUGE number of shader units(32-48-64.....) with its own 128/256mb ram but make the card very small and because theres no video out they could have the card exaust the heat out the back, design it to fit under/next to/above the 1900 seirse cards
, i hope this happens, it would rock hard imho