The new computers won't boot into OS 9, no way, no how. They will *run* OS 9 in Classic, but nothing will make them *boot* OS 9.
This is because they contain new hardware (Bluetooth, Airport Extreme, a new memory controller chip, FireWire 800) that was developed after OS 9. Apple could write OS 9 Toolbox routines to make these computers boot OS 9, but it won't--for the same reason that it did not make Power Macs boot System 6. When the Power Macs came out, System 6 was dead, and Apple no longer wanted to dedicate money and resources to it; and now, OS 9 is dead, and Apple doesn't want to dedicate money and resources to it.