Matt recently revealed the covers for two new books in the series that will be published in September this year.
Escape from Castle Ravenloft is especially noteworthy because it is the only book so far to be associated with a D&D setting other than the Forgotten Realms. All the books in the series have tie ins to current D&D Adventure Sourcebooks. The Mad Mage's Academy is tied to Waterdeep: Dungeon of the Mad Mage for instance.
More Isle of Dread material from WotC would make fans of BECMI D&D and fans of Mystara happy. The setting has been teased in numerous D&D5E books, but Isle of Dread is the only book to fully embrace the setting.
See also: An old analysis of mine about the old Endless Quest Books and possible connections to Mystara (Piazza thread)