Arkyn, in another recent "Wanted - GM's" thread:
3) Birthright setting; there are a lot of keeps out there that need to be scouted, cleaned out, secured - and occupied. A good task for a mid-level warrior and his sidekick the back-door man. Or something...maybe a diplomat between some hostile city-states, or leader of a squad to set up a fort in the Five Peaks?
I like the BRCS a LOT.
Bloodlines are not necessary to that, but do add an additional dimension, both positive and negative, for the PC's who have one, or just knowledge of their existence and how they work.
Running the game "as intended", either centered around 1 blooded character, or all associated w/ 1 Realm, or all of allied Realms (whether or not the sole Regent(s) of those realms) can be a lot of political fun.
But finding oneself blooded, and trying to forge a new (mini-)Realm can also be a great angle (if perhaps a bit involved for a typical pbp game).
So +1 for Birthright!