It's not so apparent in the book itself, but I find it intriguing that so many of the little islands in northwest corner of the full map have one or more locations marked on them. I've never heard of Vilkstead or Ulf of Thuger before, and yet they're on the map while places like Everlund and Athkatla are not. I can't help but wonder if those islands are going to get some attention at some point. Maybe they're planning a high seas campaign. That might explain why the swashbuckler is in the book.
I just recalled that Chris Perkins mentioned in that convention panel he did that one of the preview adventures he ran (that was an extension of an upcoming AP) was the PCs dealing with barbarian ancestral mounds. Most of the Uthgardt mounds are in and around the Silver Marches, so perhaps the main AP is up there in the northwest like you said? Viking/barbarian/high seas in those northwest islands might make some sense. And if that's possibly the case, it could also push the Ravenloftish AP (assuming that is happening) to next fall for the Halloween season like several people have surmised. The Warlock's Crypt thing might be that Raveloftish horror location perhaps? Or maybe it's the entry portal into Ravenloft itself.