The CPU and GPU arn't a good combination to combine.
They tried it with intergrated graphics and look where that ended up.
It would require an entire new motherboard architecture to reposition memory and even more cooling before it would be fast enough.
Another thing: I don't think using the GPU would be good enough for the browser, seeing as the OS interfaces with the CPU so whatever the GPU processes it has to send back to the CPU anyway.
Another, other thing: Intel ATOM processors arn't that fast, they truely arn't designed for desktops. They're low power and suited for netbooks / laptops. Desktops need power hungry Intel desktop processors

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