With the new PSF system, and due to the fact that this is a "supermod" i think there's a couple things about diplomacy that should be tweaked. I think these modifications are far from being impossible to implement, and the first one is particularily important, since playing without is could reveal to be a pain in the b**t
1)[PSF MILITARY ACCESS]
What i am talking about is the fact that, since it will be possible to have PSFs in allied regions I believe the old option of "Military access" has to be modified: In the previous mods allies were far too asking when it came to accepting to give/take military access. What i mean is, for example, if i am playing as hungary, and have a couple of PSF in a polish region, while Poland is my ally, i don't want to have our relationships to get constantly eroded by my troops moving around his country. Therefore i think that if the two factions have equal power they should accept exchaging "military access" as it would be a fair trade, or if one of them is more powerful than the other, it should also ask for something else in return, within reason. Alternatively you could totally eliminate the diplomatic penalties due to army movements in NPC regions (but that would not be realistic).
2)[JOIN WAR]
You implemented the "claimed rebel settlements script", where capturing a settlement claimed by another faction automatically meant a declaration of war on said faction. That had also been implemented in EB. But why not take it a step further? Why not make the vanilla overly simplified and boring diplomatic script a little bit more interesting?
What I am thinking about is of another method to indirectly (and thus without direct military offensive actions) declare war on another faction. Too many times we asked ourselves what that "attack faction" diplomatic option was for, when nothing happened at all even if you could involve an ally in making such a deal. Why not make these kinds of deals much easier to achieve if you and your ally are in excellent diplomatic relations or you just "convince" the ally with some monetary gifts to do so? And also, and most important, the script regarding such deals should make so that if, for example, playing as Hungary I ask Poland to join the fights against HRE, and Poland accepts, when i close the diplomacy panel Poland and HRE are already at war. (thus making that diplomatic option the very same thing the "join war" button was in napoleon and shogun).
3)[REASONABLE VASSALS]
In the medieval times there were very many small states being vassals of bigger kingdoms. In all Kingdoms mods i have found that it was far too difficult to force a small state into becoming a vassal, so even if, for example they were bankrupt and outnumbered 10 to 1, they were defying to the death. So we players would surely want the AI to be a little bit more reasonable, and accept loosing their independence (in the hope of plotting for revenge, maybe, if your king has not enough authority, or their FL is not chivalrous?). Also, since vassal states are merely duchies, and follow the rule of the king, they should automatically declare war on their master's enemies and ally with their master's allies via script, if possible. IE if, again, while playing as hungary and having the serbians as vassals, war erupts between me and HRE then the next turn the serbians will also be dragged into war against HRE, willing or not.
I really think these methods can be implemented through script (although i would not know if that script would be so massive as to slow down the game). These tweaks would also mean a HUGE change in the gameplay experience, making the game far more enjoyable with a relatively small effort (The first idea i think it is really necessary).
I know you have a lot of guys asking you to implement lots of ideas (some of which even stupid, i dare say), but these would be something never seen before in any other mod, realistic, and truly a great improvement for the gameplay.
So please, anyone who wants, comment the ideas, discuss them, tell me if they can be implemented or not.
Thanks again to the team for the wonderful job, i can't wait to see the results of all these years of modding