Fewer than 3% of hotel redemptions were for seven night stays.

If this statement by Marriott is true, then why would you change these 7 night stay packages so much. It would make sense that the people that take advantage of these packages are Marriott's best customers. I would think you would leave these alone as a way to reward those customers. It is not a large percentage of the hotel redemptions, so the impact to Marriott should not be that great.
My recommendation would be to leave the seven night packages the same for the timeshare owners and then make the five night package available to everyone else. It would definitely make things easier for the timeshare salesman that have used this as a main selling point for buying a timeshare directly from Marriott.