This is fantastic. It finally puts the FW800 models ever-so-slightly-above the other ones for Mac OS use. Back when I had the privilege of collecting multiple MDDs, I always went specifically for the MDD 2003 motherboards + the original MDD 2002 case (House of Moth elaborates on why), but I always avoided the FW800 models specifically because it just meant having 1 less FW port than the other models. But now it's the opposite, and with FW800 speeds to boot?!
FW800 owners may rejoice. 
Totally agree. In my mind, the FW800 MDD has now been upgraded from "problem-child not-as-desirable MDD" to "the most desirable MDD model".
In fact, this is what I am now envisioning:
The FW800 MDD OS 9 Hardware Enablement Pack- hardware temperature monitoring (DONE)
- native FW800 (DONE)
- functional FW400 x2 (DONE)
- native on-board USB 2.0 (DONE)
- Bluetooth (up next)
- AirPort Extreme (after Bluetooth is done)
- improved sleep/power management support (currently broken)
In collaboration with @DieHard, perhaps we can eventually develop a single OS 9 installer disc, specifically for the FW800 MDD, that unlocks all of its hardware features in one fell swoop. That would make the FW800 MDD
the undisputed king of OS 9 machines.By the way, I hear that the MDD 2003 models (not FW800) have the same USB 2.0 chips in the motherboard as the FW800 boards do, whereas the original MDD 2002 models don't. Are you able to confirm that personally, @UnexpectedBomb?
Ah yes, the June 2003 FW400 MDD. Good thought! From what I can tell, this is not a late board that inherited FW800 features, it's the older 2002 board brought back to pacify those who (rightfully) complained about not being able to boot OS 9

However, I don't have one on-hand to confirm this with certainty. If anyone does have one and can confirm, that would be helpful. I do know this June 2003 model dropped AirPort Extreme and Bluetooth, so I suspect the NEC USB 2.0 controller went with them as well.
I honestly wish we had full MDD schematics in a way so that we could order in our own custom MDD motherboards and daughtercards via the likes of PCB Way and whatnot. This would give us hardware independence that we currently lack, and keep real Mac hardware coming.
Given the speed at which AI and technology in general are advancing, this may be possible sooner than you think!