I think that a new dev-diary would not be coming for a while. Those are thematic showcases of the feature set...and the next one missing is the management simulation..that is a long way away from showcasing I think...
For reference...
Dev Diary 1 : The team talk about the philosophy behind creating a living, vibrant, and personality-driven crowd.
Dev Diary 2 : What you will be able to do with the building tools in Planet Coaster will allow you to create the next level of coaster parks.
Dev Diary 3 : Modular, piece-by-piece building allows for greater control within your park. Create something epic and share it with the community, or draw inspiration from your Planet Coaster peers!