I'd be concerned, hacking my TiVo, that some evil DirecTV killer signal would come down and fry my poor machine. They've done this sort of thing in the past with people who pirated their service, but it's hard to say whether it would be legal or not for them to fry the machines of paying customers.

Still, it would be fantastic to have video extraction, particularly of HD signals, although I'm probably more interested in having HMO functionality (i.e., use my HD-TiVo as a Roku PhotoBridge HD).