"I believe the OS itself should provide an API to the binary programs, and each subsystem (video, audio, I/O) on external chips should essentially provide a communications API to the central 8052. So a program running on the central 8052 calls an API in the OS which in turn sends a specific command to the specific external part."

Isn't this all going against the philosophy of those old home computers? They were designed to milk every last ounce of performance out of the hardware. This is beginning to sound more like a platform for windows CE.