General purpose programming on the GPU

The video-card manufacturers are at an interesting crossroads. nVidia is really pushing general purpose computing on graphics hardware.

Cool idea, but it can't really take off unless programs are written to detect the presence of capable hardware and load code specially compiled for that particular chipset. In other words, GPGPU code written for nVidia cards won't run on ATI cards. Bummer. Clearly nVidia understands the advantage to be had from a large body of code compiled for their instruction set. They want to be in the position of owning the GPU equivalent of the x86 instruction set. Nice move on their part.

But wouldn't it be much cooler for the rest of us if things were a little more open? Is a common instruction set for graphics cards at all plausable? Like ARM is for embedded devices? Or maybe a common intermediate layer and JIT for all types of GPU code? That would be cool. And something like that would induce a lot more developers to take the plunge into compiling to the GPU, which has got to be a fairly drastically different piece of code relative to a straightforward implementation.