As far as DLC's go, I think more classes and a higher difficulty is a natural choice as well as expanding the evil playthrough.
But I'd love story DLC's to explore ending story options for companions.
Ideas:
1. Re-forge the Crown with Gale.
2. A journey for a cure for Vampirism for Astarion (only available for spawn). Possibly bring Jaheira since she knows about it? Could be an option to bring Minsc too (with really funny dialogue about how much Astarion hates him lol)
3. Bringing Shadowheart back to Selune and possibly incorporating quests with Isobel and Dame Aylin for that.
4. Flying back with Lae'zel to fight the forces of Valkith if you're a Gith player or you've earned their respect (only available if Lae'zel rejects Valkith).
5. Any chance to have an actual companion quest for Minthara.
6. Instead of getting Wyll out of his contract the weird and half-baked way it happens in-game, make it a quest to return to Avernis and incorporate Karlach's story into it.
7. Naturally, a companion party/get-together either before the final fight or after with extra romance scenes and see the companions interact with each other and see them have drinking games, fun conversations. I'd love to find out how they all feel about each other. (draw from Mass Effect Citadel DLC; its a gold standard example.)
8. Something for the Dark Urge character possibly post-game that includes an extensive journey to control the impulse. Include companion reactions to your journey and possibly make it emotional for your romance.
