I've always thought, that if Dagna was a LI, she would be tied into the Cadash origin story. Mainly dealing with the fact that the dwarven inquisitor can now do magic (kinda).
Technically I guess, one might consider being a Grey Warden a form of "magic" seeing as how it does give you dreams, something dwarves usually lack. It's been shown time and time again that dwarves can interact with the magical realm if given us enough of a push.
If she does have a major role in the game, I hope at least part of it will be figuring out why dwarves are so different from the other races of Thedas, and what it has to do with their connection to the stone. It's a subject that has always fascinated me.
I dunno if she'll be tied too directly with the Cadash, wasn't it said that s/he was part of the coutorie (I've got not clue how to spell that) or something? Not something Dagna seems inclined to get mixed up in.
@TheodoricFriede
It would be nice if Dagna turns out to be a romance option but I don't expect it. She could be race gated and bisexual. At least than race gating could work in the favor of dwarves instead of mostly against, as I am fearing.
Since I've always looked at things from the perspective of Varric being a romance option, I've always thought of race gating to be in the dwarves' favor, but that's a lot of wishful thinking on my part.