For me, there's tons of info in the books already published, as a GM, I am working hard to pull every shred of info on the numerous powers (cults, dragon lords, essence lords, unlife, religions etc.) in one place to be able to make sense of what is really going on in Kulthea in any given area. What would be very handy for me as a GM is a large tomb containing all powers (almost like a 2nd edition powers of light and darkness on steroids).
Each 'Powers' section might provide the following:
Names and titles known by and by whom (if applicable)
Goals of power
Strategy to achieve goal
Major tactical actions engaged in or about to be initiated (list of key trigger events)
Influences on power (Names of other powers actively subverting or influencing)
Active spheres of influence (on other powers or realms/kingdoms)
Key allies and enemies
Operating locations across Kulthea and relevant tactical information (i.e. overview of action's in play or about to be initiated)
HQ Location (stated by continent, realm/area and settlement)
Key behaviours of power (method used; to engage, subvert/attack/influence, retreat)
Breakdown of power's forces and stats
Hierarchy within power (something like an organization chart)