The first possibility is to make the text physically unlimited, in the sense that a story can be enriched by the successive contributions of different authors and in a double sense, let us say either two-dimensionally or three-dimensionally. By this I mean that given, for instance, Little Red Riding Hood, the first author proposes a starting situation (the girl enters the wood) and different contributors can then develop the story one after the other, for example, by having the girl meet not the wolf but Ali Baba, by having both enter an enchanted castle, having a confrontation with a magic crocodile, and so on, so that the story can continue for years. But the text can also be infinite in the sense that at every narrative disjunction, for instance, when the girl enters the wood, many authors can make many different choices. For one author, the girl may meet Pinocchio, for another she may be transformed into a swan, or enter the Pyramids and discover the treasury of the son of Tutankhamen.
This is today possible, and you can find on the Net some interesting examples of such literary games.