Seems kind of unlikely - the normal threshold is 32 MB, I believe - it takes that much memory to do the Quartz Extreme thing, which is, after all, to put the entire job of operating all video functions on the back of the GPU.
If you have an AGP G4, the best path to Quartz Extreme is a Radeon 8500 Mac Edition.
They could write Quartz Extreme for Rage cards, but you would see almost nil speed gains from it as Rage 128 cards can only map square textures.
In simple terms this means that if you resize a window to say, 240 x 360 pixels, the Rage card is going to render a 360 x 360 pixel area, which is quite inefficient. You might see some gain with the processor being a little more free'd up, but the Rage GPU is going to choke on all the drop shadows and transparency and Aqua is going to feel just as sluggish as it would without QE, which make the whole endeavour pointless really because QE was designed to speed up Aqua.