How I could see this work: the Inquisitor is invited to the opening night of a special play chronicling the destruction of Haven and their choosing by Andraste, but due to a mix-up only gets two tickets. You can bring any companion you want (though obviously only companions you have currently recruited) or one of the advisors. Much amusement comes from the hilarious mistelling.
At the first act intermission, the Inquisitor either receives a message about some fiendish plot being cooked up at the theatre, or notices some odd magical goings-on. The Inquisitor investigates, and a low XP solo adventure ensues culminating with them arriving on the stage to confront the villain. Upon defeat, they get a standing ovation. The play goes into hiatus because most of the actors were horribly injured, and the DLC ends with the Inquisitor's "date" thanking them for a lovely evening or making some other amusing comment.
Now -that- sounds adorable. XD
I'd honestly love any kind of extra character interaction DLC. You owe Cullen a rematch at chess (or whatever game that was), there's the round of Wicked Grace Varric mentioned. I mean, come on! You can hang out with Sera on a rooftop anytime, why not play a game at anytime with Cullen, Varric, or Josephine? Have a drink at the tavern with Bull or Blackwall? Add some diverse conversation, debate over recent decisions, or personal information from both sides to it and I'm all over it.
I'd also like to see a real party (not quite Lelianna's idea of a "real party") at Skyhold - outside. A big feast day with music, dancing, tournaments/sparring, and cultural themed events. I wonder what Dalish music would sound like and how they party.....