After talking to a lot of folks on the BSN, party combition matters little. Folks have put Sera and Cole in their party together, along with Vivienne and have gotten either maybe one banter in their 40+ hours of game, or none at all.
I spent most of the night testing to try to get the banter to work. The only things I haven't tried now is reinstalling the game, and rebooting my computer. I'll try the latter next, but otherwise I'm running out of ideas.
This is what I have and haven't done on this latest test dummy, another dwarven rogue archer. This was after yet another repair attempt:
1) Deleted and recreated a new world state, using the same options
2) Barely looted anything during the very beginning, except for the nice hat right before the end of the Temple sequence at the beginning.
3) Choose a couple of different answers than last time.
4) Acquired, but did not equip the dragon weapon and armor set.
5) Immediately turned around after the first Haven cutscene to talk to the War Council.
6) Immediately went to the Hinterlands and to Harding's camp.
7) Did not go to the Crossroads, or talk to anyone else.
8) Waited about 20 minutes at that first camp.
The result? Varric made a single comment about 2 minutes after the end of the conversation with Harding. He made a comment about the refugees reminding him of Kirkwall during the riot. Otherwise, there was only complete silence save ambient sounds and music. I'm feeling really disheartened right now. I've got some more ideas I'm going to try, but not for tonight. Tonight, I'm just saying "screw it" and getting ready to go to bed.