There's going to be a new festival in 1.6! Along with more dialogue, new items, secrets, and "???" whatever that means. Also previously confirmed was an iridium scythe and big updates that are supposed to make modding the game easier.
Usually when you see sudden news about content from old games it means that the business behind it decided to cut off the plug. ConcernedApe is one of the few devs where the news are the opposite - "I wasn't planning to add more content, but..."