This is hardly a "familiar" architecture to Amigans. There are a few things you should keep in mind about the Amiga and "PC" coprocessors:
1) On the Amiga, the CPU and chipset have to share memory. Yes, they have their own address spaces, but they don't have "dedicated" memory. Modern PCs use memory controllers to keep the main and sub processors from conflicting with each other or wasting effeciency, or have their own local memory. The Amiga isn't even close to what is being done years ago, let alone today.
2) The Amiga did not have sufficient abstration layers to use the custom chips effectively. Hence, the sheer mass of games that won't run on AGA. The reason why multi-processor architecture works is because of the software layers that can shift responsibilities between different architectures. Commodore wasn't even close to making their own DirectX.
3) Dedicated hardware is expensive, and if you don't use it, it goes to waste. The reason why AMD was so keen on purchasing ATI is because, ironicly, the CPU and the GPU are capable of very many similar tasks. That means consolidation of the architecture improves efficiency and performance, at least for the low-end. This is also why the physics and AI coprocessors will flop horribly. Of course, consolidation isn't a good idea in the high-end -- Sony's Cell processor is perfect proof of that.
I'm not sold on this multi-processor idea. Unless all the hardware is perfectly synced, you're going to have a lot of waste. This is especially true if, for example, you want specific ports that aren't built into the motherboard. The whole point of a motherboard is to offer the basics and accept daughtercards that do the specialized stuff. This multiprocessor idea is more along the idea of a game console than a PC. Flexibility is what PCs are all about.
