I'd rather hear Cullen mentioning things about Kirkwall, Hawke and the companions that we didn't get to hear from him, new insights about what he thought about it/them during the whole thing and looking back. But if he mentions the mage Warden, I hope they add something to it. Maybe he can mention any Warden and talk about his experience in the Broken Circle quest instead.
If that trailer is accurate and Morrigan and Cullen meet at some point, it'd be fun if a Mage Warden import caused them to have a radiant conversation about Amell, we are able to overhear (and possibly join in with).
For a male Warden who romanced Morrigan, Cullen's reaction to learning that the rumours of Amell's involvement with the Witch were true, while for a female Warden who befriended her, I can imagine Morrigan noticing his wistful tone when talking about her and taking a moment to tease him about it.
Cullen could even bring up his dealings with Hawke, the events of Kirkwall and joke about how trouble seems to follow that family around... and cue a moment of awkward silence if Morrigan did the Dark Ritual with the male Amell...
But since that's probably too much, I'd settle for just a comment about Morrigan still wearing the rosewood ring if romanced, what the Warden did at the end of Witch Hunt, or Cullen reminsicing about the events of Broken Circle.