Yay! Are we talking dwarf-y wishlist for the next game?
I think Harding has a lot of potential. She's interesting in the fact that, unlike Varric, she really has almost no connection to dwarven culture at all. She was a shepherd in the Hinterlands. A surfacer from birth in a human ruled kingdom with a very un-dwarf-like job. I think it could be very interesting to have her as a companion in a game with strong dwarf connections.
I really hope that they explore the Ambassadoria in depth in DA4. It's such a unique and different facet of dwarf culture that I would be gutted if they skip it (or, worse, just have one mediocre quest attending to it). Also, Kal Sharok could be on the table as well. Personally, I'd like them to focus DA4 solely on the Imperium and Seheron (there's enough there to fill a full game) and to have the Anderfels, Nevarra, and Kal Sharok as the following game. But, given it's proximity, it's not out of the realm of possibility. So we could be exploring both the Ambassadoria (well, more like learning about it and interacting with them since there's not much 'exploring' to do) and Kal Sharok in the next game. Wouldn't it be interesting to bring a surfacer dwarf with us and see how that changes her self-image based on finally experiencing her race's culture(s) first hand? I just think there's something interesting there that could make a compelling dwarf companion storyline. Especially since "personal journeys" are pretty common for LI's and, if she returns, I'd put my entire paycheck on her being a bisexual romance for all races.
I would also love to see a member of the Ambassadoria. I think I've mentioned it somewhere before (maybe in this thread), but I have this idea floating in my head of an ostentatious and foppish Ambassadoria member who would join your group as a warrior. On the surface, he'd be vain and effeminate and a bit bourgeoisie (in the Marxist sense) (I imagine him being a bit like Zidler from Moulin Rouge or Lyle from Penny Dreadful) but then he'd also be a shrewd and cunning politico as well as a competent sword and board warrior. It would just flip how dwarves are perceived a bit. And, I'd like him to be a non-romanceable character (and straight -- just to **** with people's perceptions again).
Finally, as I make very clear in the KISA thread, I'd love a Rock Knocker in the next game. A strong, proud, dwarven warrior who (for some reason) has ended up as a Rock Knocker. I could easily see some storyline where he volunteers (as tribute...) to join the order for the honor of his family, which would potentially free him up to be able to choose to join the PC's entourage. I see him as a typical duty bound noble dwarf (Gorim style) and, of course, a romance option. And, even more of course, available to other males (and females too, I suppose, since we all want our dwarf LI's, right?). 
I know it will never happen but could you imagine how awesome it would be to have all three of these characters and be able to run a full dwarf party! You'd just need to make your PC dwarf a dual wield rogue and you could have that (PC), a ranged rogue (Harding), a sword and shield warrior (Ambassadoria), and a two-handed warrior (Rock Knocker). Who needs magic when you're rolling with that crew?
Sigh...... I'm going to go revisit my current dwarf warrior playthrough on DA: I. I need more dwarves in my life......