About the Shadowheart is a Selunite theory: I had an interesting conversation with her, when her hand started glowing. As a sorcerer, you have a special dialogue option and she basically says something about how that light is familiar to her - I mean, that could mean a lot of things, but I had to think of that theory, when I heard it. The new lines, they gave Shadowheart, really made her much more endearing to me. SHe was my favorite before, but now, a lot of things make more sense. And I do like, that you finalyl get a glimpse at what the artifact is capable of.
Exactly and to add to that theory, Shadowheart also says she doesn't have her memories. If she happens to be a Selunite, I wonder what happened. There is definitely something mysterious going one. It's one of the reason why I like her character because there is a level of mystery around her.
I think, according to lore, it isn't that uncommon, that Shar worshippers have their memories taken, but in this context, there is certainly a lot of potential story in it.
"We are all stories in the end. Just make it a good one."