Really liked this thread.
Here's my suggestion about the declaring war and diplomacy thingy:
First of all all fiefs should have it's own borders like total war series.
Now this :
Add diplomacy tool for strategus.
Like "buy menu","transfer menu" add a "Diplomacy Menu" where you can arrange agreements with other factions.Also you can send pm's to each factions designated members (Rank10 members let's say.)
You could send propositions to them which are linked to game and locks,unlocks some of your movements if agreed or declined.
Some examples that i can think of now :
1-Military Access Granted for armies consists of troops lower than #
If enabled, you can enter this faction's lands, if you enter a factions land without this agreement your faction will get some -Fame points.
2-Declaration of War
You get + fame points and after 24 hours you automatically grant acess to your targets lands and you can attack their fiefs without -fame penalty.
3-Entry of fiefs enabled,disabled
If a faction enables this for your faction/individual, it means you can enter his fiefs.You cannot use a faction's fief if it doesn't allow you to. This option is only available for factions who have + 50 fame points (Example)
4-Production/Recruiment bonus by Fame points.
Some Examples of Results having negative fame points:
If X Faction has -50 fame points lets say:
Other factions won't get any negative fame points if they enter your borders without signing
"Military Access Granted for armies consists of troops lower than #" agreement.
If X Faction has -100 fame points:
Other factions can attack X Faction without declaring war and waiting for 24 hours.
Please share your idea about this system and also tell me if its possible to implement sucha feature.