These are all good suggestions. I think you're right, and that the key is whittling down the story to a more simple conflict that it can be "about", rather than that conflict being the whole Fifth Blight. Over on the LJ side, here_be_dragons suggested that the conflict could be who is taking leadership of the Ferelden Wardens, which would allow me to put the focus on the two dwarves (whether they be Sereda and Kasia or two new characters created specifically for this story -- I had been planning on the former but now I'm think that the latter would allow me greater flexibility) rather than making it so epic in scope. It's a good idea, one that I need to think on a bit.

Picking and choosing quests to cover the whole Blight is also a possibility, but that's less interesting to me than picking one aspect to cover more in-depth.