Okay, if dish is hinting at it, this is my guess how encryption works on the 721 and 921. We know already that Dish decryptes the signal from the sat and then encryptes is again via the DVR functionality built into the broadcomm chipset. While a lot of effort goes into the CAS (Conditional Access System) on the sat content, my guess is not nearly as much goes into the system on the DVR it self. Afterall, you have to have paid for the programming in order to view it. The DES encryption on the drive is really there to keep you from extracting programs from the HD.
Afterall, you might put this Digital signal with half the PQ of the Analog feed from a BUD system on the internet.
At any rate, IF Dish uses the same DES keys on all the 721 and 921 units then they could shuttle around encrypted video between units. It's still not playable on you PC.
The max speed any network adapter would get is 12Mbit/sec Or 90 Megabytes per minute. And that's most likely wishful thinking. You could certainly send SD programs to other people. And Dish needs ZERO time to get networking working on the 721 or 921. The webserver that hosts the GPL code at dish runs on a 721.
The tech for doing it isn't hard... Until lawyers get involved. The recent FCC ruling may give a helping boost there, BUT dish does need to focus on getting the quirks out of the 721, and just getting the 921 to do what the spec sheet says it does.