I would like it if Apple put this into the MBP as a co-processor. I had a lot written, but then I realized, what if Apple makes the i7 a co-processor, and uses the A4 as a main CPU. It certainly has the horsepower for mundane tasks like surfing the internet and word/excel. Then, when you need the extra CPU boost, the core i7 powers on. This would also allow the MBP to sleep for great lengths of time, like the PowerBooks could.
Interesting point. To be honest, with the far better power management in the i-series of chips, especially the later ones, an i-series mobile chip shouldn't be taking much power on standby anyway. Perhaps even almost as little as the A4.
Issue 1. Standby power isn't just about the chip, it's also about keeping the RAM alive. Laptop DRAM is bigger and faster and takes more power than mobile device flash RAM, which is able to sleep on zero power. The laptop mobo also needs some power, as does the Wake-on-LAN feature and whatever else drains some juice.
Issue 2. How would the A4 be integrated? The macbooks are Intel devices, with Intel chip on an Intel mobo. The two form a tightly bound whole. There's no way you'll be able to get an Intel mobo to support an A4 chip, and ditto the other way round - the A4 mobo won't support an Intel chip either. The only way I can see it being done is for each chip to have its own mini motherboard ...
Issue 3. A large part of the power of a laptop or desktop chip comes from it being well fed with data from large and speedy DRAM. Take the DRAM away, and use flash RAM, and the fast chip is basically crippled waiting for data. So you've got to either have DRAM and keep it powered up, draining the battery, or leave it turned off, and have a pause while the DRAM is woken up and filled from the slow flash memory, or not have DRAM at all and cripple the fast chip.
Given all these tradeoffs, it's hardly worth it.
