I couldn't even begin to imagine how a quest for Scribbles would go? She's political, right? So maybe we have to accompany her to some boring thing that goes ****** up and then we have to fight/sneak/whatever our way out? Leliana is a rogue and Cullen a warrior, so it's entirely possible that Scribbles is a mage.
I'm now wondering if maybe that quest we saw with Leliana might be interchangeable depending on who's approach we picked for taking it? I mean, the plot itself seemed more central to Dorian since we were dealing with his old teacher (or whatever you wanna call him), so I'm not entirely sure why Leliana would be there? It kinda seemed like she was there to help, so maybe if we had picked Scribbles approach instead and she went ahead and tried to negotiate with the enemy instead then she would have been there, or if we'd taken a militant approach them it would have been Cullen there instead?
Possibly the quest changes a bit depending who you send.
Though I don't think the quest is Dorian-related. Darrah said it happens after a series of branching events in the mage-templar war. It seems it'll be a critical path mentioned by Darrah, about this plot.
I think companions, since they're related to certain plots, will give a better hindsight if brought along in those quests. I wonder though if not bringing Dorian will cause problems though.