I guess that stretches the definition of flirting to non-meaning, for me. If all it means is friendly repartee, then a lot of people are flirting without knowing it. And would be pretty shocked to hear they are. 
But, possibly I'm just reluctant to jump on "ship" bandwagons because it seems like half of fandom is about that and it's often so silly. I find their mutual understanding surprising and moving. Don't hear anything romantic, nor could I see that ever happening even "in another world."
I know this discussion is dead but I'm reading all of the posts I missed!
I agree with you Addai. I'm a generally nice person, even to people I don't like, just.. Because. Same for my boyfriend, a (generallyyyy) nice person.
My boyfriend has been 'accused' of flirting with girls he's been nice to. Several times. It really pissed him off (something on lines of "just because I'm being nice to her she thinks I'm trying to hit on her? I have a girlfriend!"). He can't even help women on the bus without getting a snarky comment and an evil eye (so he stopped).
I'm certain guys who I am nice to think I am flirting with them, but I never flirt, NEVER. I didn't even flirt with boyfriend, I don't even know how to flirt!
We have a group of friends we hang out with, it's consisted of females and males. Everybody's nice to each other! Most of us have a bf/gf. We even, god forbid, hug! We even poke each other (not me, I hate touching, but that's besides the point).
It's completely OK for males and females to respect each other, be nice to each other, and even touch each other all the while not flirting.
This is something that has an example in game. Cullen? The flirt options for him? It's being nice, it realllllly bothered me that in order to feel like I'm trying to befriend him and be nice to him I need to "flirt" with him :|. When it was in character I chose the flirt option because my PC respects Cullen and likes him as a person. Same with Dorian, I wanted to compliment his sense of style! I wanted to be nice to him because he is so so easy to get along with. Why do I need to flirt with him for that? At some point I stopped because I didn't want to get a silly "I'm not attracted to females talk" (I din't know if one exists but.. still). Why is it easier to be nice to Varric just because he is not a love interest?
Anyhow, my point. Grownups can compliment each other without it having hidden messages behind.
I think Solas and Cassandra have great dynamics and chemistry, but they are too different to enter a romance. They are both open minded people, and it's wonderful they can converse and be respectful of each other while not feeling the pressure to change their beliefs. Maybe if Cass wasn't so religious and forceful (Solas generally dislikes unnecessary violence) and Solas was less of an.. elitist god, then perhaps. But these things are what makes Cass Cass and Solas... Solas.
/rant