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Because both CPU and GPU are generally on the same bus in mobile devices, maybe you could use those extra CPU cores as fragment/pixel shaders, if memory and cache architecture doesn't prevent it.

On PCs that is not feasible, because of bandwidth and latency issues over PCIe. On mobile SoCs, who knows, maybe it'd work.

Just like in current PS3 titles, that offload shading from GPU to SPUs.

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PS3 games don't offload fragment shading to the SPUs, that would be too slow and leave the pixel shading hardware on the GPU idle. Remember that the PS3 has separate vertex and pixel shaders. What they usually offload is post-processing, mostly for anti-aliasing.

I was talking about a technique where deferred rendering, GPU is used in modern PS3 games to render surface normals, material index, Z-buffer, texture color, etc. in a buffer. Typically 128 bits per pixel.

This buffer is then DMA transferred to SPUs, where final lighting and fragment shading is performed.

Final step is to transfer 32-bit RGB data back to GPU's frame buffer for displaying.

Here's a link about one implementation: http://www.slideshare.net/DICEStudio/spubased-deferred-shadi...