I asked them about that last year while on board - they said it had been discussed, but they weren't sure they had enough programming or whether DVC staff members would want to be gone that long, etc. I am guessing that, if enough people request it, they will consider it, unless they somehow already know that people either buy in the 1st four days or not at all. Seven days should allow for more selling time. They may need some ideas for what to do on the 3 additional days - more days at sea - more ports - more iterations of the guest legends / inspirations. Not so sure it would be just a standard Magic itinerary, but I would be interested in a 7 day, too. More time to dine at Palo's, socialize with other members, etc.
As for 2009, I started talking my brother into considering it. It aligns with his regularly scheduled Sep vacation, and I told him there were stone crab claws at brunch. Quite sure it was the crab claws, as he and his wife have never seriously considered any cruise before. And yet, I don't know that I can swing two cruises in one year.