Well said. Hopefully during the DLC we'll be able to learn more about what it truly means to be Dragonborn. I also want see if our characters are really a Shezzarine or not.
Like most quests, there is room for depth. Beth just has to explore it. This undead priest slightly reminds me of the Underking as well, so there's also the Talos angle. The key that will make or break this dlc in terms of story is how many times we run into this Dragonpriest character. If its just once, it'll probably flop. But if we run into him a lot, and get to talk with him as much as we talk with Serana in Dawnguard(if not a little more hopefully) we'll actually get to form an opinion on him and the story will be that much better for it.
The dialoge doesn't have to always be plot related either. I'd love it if these two characters went of on a tangent and just talked about what it's like being Dragonborn. That would be so huge for both the characters involved, I can't even begin to explain. Idol pvssyr builds character. We'll get to know his likes and dislikes. Even something as simple as that can make a world of difference.