I still see Cullen being the party member route. As Lob mentions, if you are anti templars it wouldn't make much sense for your military advisor to be a templar. Party member sure, but I don't think you put someone you have that big of an ideology split with in charge of your soldiers.
It is still working on an assumption though. The idea that there are advisors and such in this manner. For all we know Leliana is just your go between for you and the Chantry. I believe all we know for a fact is that she like morrigan won't be a party member.
In the previews, the type of Fort you build affects some aspects in ways we don't know and how many agents you have to do missions. The person you talk to for updates in the video is just some no-name soldier.
Its an interesting theory though.
When I first mentioned something like this on another thread I based my claim on a leak ( not the companion one ) that stated that the Inquisition will have 3 other lesser organisations or somethin like this with whom it will interact.
The Iron/Red Fists (can't remember the actuall name) - military
The Golden Keys - Trading.
The Purple Crows - Espionage
When it comes to The Purple Crows, it said that Leliana is their leader. I think it also said that Scribe Girl is a representant of The Golden Keys and you can also see a golden key symbol in a screenshot from the PAX Demo
Don't ask for a link. That info was swallowed by the dark depts of the internet. I actually saw a screen shot with that info.You'll just have to believe me (or not)
It also said things regarding The Red Templars and their antagonisitic nature before any official information regarding them surfaced. I don't think it's 100% correct by now, but some info proved right so there is a grain of truth to it.
Why do I think Cullen is the military representant? If they go on the 3/3/3 route, there is only one othe place for a warrior. There is Cass and The Iron Bull. Between Feathers and Cullen I think that Feathers fits better as a companion. Cullen seems to have more connections to the loyalist templars and maybe other military guys while Feathers might be a warden that abandoned the order.
If they don't go on the 3/3/3 route then I can actually see Cullen as a companion.