Myst Online - Episodic Content @ Official Site

The official Myst Online site has more on the upcoming transition to the release of episodic content.

Based on your feedback and in-game actions, we are making some big improvements. Starting with the next update, we are making the move to regularly scheduled episodic content release. By having a set schedule of updates, players can be ready when major events will be happening in the cavern. That means that the release of all of an episode's content and story (e.g. new Ages, pages, clothing, character interaction, story revelations, artifacts and intrigue) will be packed within a single week each month, rather than spreading out the releases over the entire month.