You can't just take the motherboard apart, cram in a new SoC (even if you were able to get your hands on one and the pins fitted) and expect it to work. That's why these are called embedded systems.
Off-topic: Also, Broadcom produces arguably superior (but more tightly integrated?) GPUs than Imagination Technologies. Too bad they're coupling it with that joke of a CPU but hey, maybe they'll upgrade the design some time?