Obviously we are all still guessing to a degree, but I believe the following will occur based on what i know about the MVC 2010 rollout - stay with me here:
1) Developer units (and requaled units of all types that now have star options prior to 8/8) will be "enrolled in Abound" for either free, which is what i believe, or a very modest fee, sub $500. This is how MVC treated new and resale MVC points purchasers after the rollout. Even with the junk fees, overall its not a bad price, and people still buy resale MVC points.
2) the non requalified mandatorys that have SO use prior to 8/8 that will be given the "opportunity to enroll" will require a fee, probably between $500 and $2,500, per account not per unit. but will then be washed clean and will be full members of Abound. These units are similar in many ways to the holdouts that owned their Marriott weeks pre 2010 that decided never to enroll, in that they have not decided to enroll but could if they chose to spend that money.
3) Whether or not non requaled voluntarys will be allowed in without a new MVC points purchase, my guess is this will only be available with a full blown MVC purchase, kind of like how the Marriott post 2010 weeks are treated today, and the reason i think this is because they are most like the Marriott post 2010 units in form and function - the voluntarys have no SOs, so you either use your home week or trade in II. They were bought knowing that. much like the post 2010 Marriott weeks, and therefore these will be strictly pay to play.