I HAD the same problem. On my first playthrough, with a female character, I wondered why dorian had no personal quest beside the Venetori one. On my second playthrough I played a human male and tried to romance him, but 35+ hours in the game and there was still no personal quest. I searched the internet and found out that the romance was bugged...great.
But I didn't give up and created a new character and it worked. I did the following steps:
- Sided with the Mages and talked about everything with him in Haven.
- I left Skyhold immediately after Haven was destroyed (I didn't talk to anyone I just left and came back)
- Talked to him in Skyhold upon my return which triggered the "One moment you're trying to restore order in a world gone mad" speech scene.
- Then I talked to him directly after that and the Felix letter scene startet
- Then I walked down into the main hall and there she was - Mother Giselle
In the other two playthroughts I chose the mages, but I first talked to him and judged Alexis, before I left Skyhold.
Thank you so much for this; it helped a lot.
For anyone else struggling with this, I tried loading my earliest Skyhold save and followed this. I got nothing. After the "Order in a world gone mad" cutscene, he started with his "It's just occured to me that you're a mage" speech, and after that, just a regular conversation with no cutscene. For the record, my game so far had been:
Allied with mages > didn't speak to Dorian in Haven > Corypheus must be stopped > Didn't judge Alexius yet
I decided to load up my latest Haven save, talk through everything I could with Dorian there, then play through the attack and intro to Skyhold again. This time it worked, I got the letter cutscene after the "world gone mad" cutscene, and Mother Giselle appeared in the main hall. The only difference between my attempts was that I exhausted my conversation options with Dorian in Haven instead of not talking to him at all.
I suspect, based on things that other people have said about Dorian talking about what you've done with Alexius and the like, that the letter cutscene won't trigger if Dorian can start his conversation with anything but the default. In my case, this would be the "I've just noticed you're a mage" intro.
Now to replay through the 40-odd hours I've just rolled back.