Well, I don't have enough knowledge on the boot process of RPi. However, I do expect that most modern hardware, e.g. x86, do not work like RPi, so your words do not hold in most realistic scenarios, at least for now. Besides, do current GPUs (not only GPUs on RPi) have the ability to self instruct in order to achieve what you said?
Doesn't the Raspberry Pi's GPU boot up first, and then the GPU initializes the CPU?
With this technology, we've eliminated the need for that superfluous second step.