I think there are enough Ravenloft adventures to fill the book. The House on Gryphon Hilll, Feast of Goblyns, Ship of Horror, Touch of Death, Night of the Walking Dead, Thoughts of Darkness, From the Shadows, the RM series of modules, and so on.
Sure, most of them aren't household names, but I would argue the same for a majority of Saltmarsh's adventures. As long as there is enough content for a Ravenloft themed campaign, I think they make it work.
And yes, PC options did not appear in Yawning Portal, but Saltmarsh proved to me that they are not above including content that is at least Player adjacent with the ship rules and backgrounds. I don't think two subclasses are out of the question.