What if it doesn't end on the Last Page?

For those of you who haven't read Jonathan Strange and Mr. Norrell by Susanna Clarke, you've missed a mid-brow piece of addictive literature about two English magicians during the industrial revolution in Britain. With lots of references to Arthurian canon and a bit of artistic license with history, Clarke has created an immersive world. The world does not end with the last page of the book, however.

Clarke continues to continue the lives of her characters online. In an interesting piece of metafiction, she describes her characters' responses to the publication of the book the details their stories.

Producing an entirely new addition to her literary work, Clarke has taken the unusual step of blending the digital and analogue literary worlds. Because she (as the person of the author) retains some level of authority, the digital presence of her characters cannot be separated from their presence in the book. In a rare way, Clarke has exemplified the idea that books do not end with the last page of the book. Instead of finding this lack of ending in the secondary productions of culture (criticism, commentary, discussion, etc.), Clarke continues the life of her novel by creating more primary productions in the digital space.

Could authors maintain interest in between books (which tend to be large, discrete productions that occur with large periods of time in between them) with digital productions of supplementary primary material? Can primary digital material function as a transition between two different books? If an author is creating primary material as a dialogue in between two books, how can that primary material affect/detract/add to the production of the new work?