Will 3D cards live forever? It is difficult to say. Performance levels of 3D chips today (or should I say tomorrow ?) such as Savage4, TNT2, PowerVR 250 and Voodoo3 are closing in on each other. Surely there is a difference in performance between each one of these chips, but it's a lot smaller than a year ago. More and more emphasis is being put on supporting features such as, 24/32-bit color, 24/32-Bit Z-buffering, larger texture sizes, better overal image quality, texture compression, multi-texturing, hardware bump-mapping, etc. Not everyone, however, is doing this. 3dfx is an example as they are not supporting most of these, but most other chip makers are pushing features over performance. I think this is a good trend, since performance from all cards is more than adequate for your standard gaming needs. Most people can't even play games at 1280x1024 or 1600x1200, so this isn't all that important for now.
There are some features which aren't fully used by today's
games. Things like bump-mapping, texture compression, 32-bit color support,
and large texture sizes (512x512 - 2048x2048) aren't used now, though
they will all be prominently featured in many new games this year. Expect
more advanced filtering tecniques such as anisotropic filtering and trilinear
filtering for OpenGL games, which will improve visual quality, though
gives a performance hit on current hardware (or is still unsupported).
This calls for features that aren't even implemented in hardware yet.
Features such as quad-texturing, which hugely improves performance in
games that take advantage of multiple rendering passes. So, as far as
features are concerned, we have a ways to go.
There is a theoretical maximum to how many polygons can be displayed onscreen. If the number of polygons equals the number of pixels available onscreen, then it's a little pointless for there to be more, since it's impossible for there to be any improvement. You can go to higher resolutions, but this is also limited because the hunan eye will reach a point where it cannot percieve more detail on the screen. The human eye cannot see beyond 24-bit color. At this point, the pursuit of more quality becomes pointless, because polygons were originally invented to fill up large portions of the screen. They were never supposed to be as little as a pixel. So when (or if) this happens, 3D card manufacturers will have to push more features to keep selling new cards, or think up new ways to render 3D scenery. This will surely happen. But what happens if these new techniques aren't sufficient and they have to think of something else within a couple of years? What if they can't think of any new ones? What then? This may sound a bit stupid, but looking at 2D today, it's really the same story.
If all games in the future support 32-bit color, massive texture sizes, a bazillion polygons and God knows what else, then what's next? Will game developers just release as many games as possible without looking at content, or will they finally start concentrating on their content instead of technology to sell their products? This could turn out pretty good for us.