I'm having a hard time getting one in the first place. And if you want one, the early ones are the ones to buy, I understand, because the chips were rushed and they didn't lock out extra capabilities it has. Next rev of production will have the extra features locked down.
Now, what they are, I haven't found out yet. But this was told to me by an employee at one of the parts suppliers.
From what I gather, they're not capabilities that would be seen in the standard Xbox 360 environment, but if you were to hack the hardware for other purposes, the early ones will have more capability. Might be an interesting find for those that like to put Linux on things.