When the 50 years of celebration promotion ends, a new promotion called "Year of a Million Dreams" will begin. The goal of this promotion will be to plus the experiences of a few select guests, some chosen randomly, with unique experiences including a chance to spend the night in the Cinderella Castle Apartment.
The apartment was original intended for the Disney Family when they visted the park. However, with the death of Roy Disney the apartment was never completed, until now. (Link)