I like the idea of titles, I'm not very familiar with SoI though, does the title exist only as the bonus, or is it displayed somewhere like in the DCN or in the diplomacy screen?
While a few of those titles are good, I think most of them are too huge and kind of unhistoric for civs. Also,
The only problem I foresee with that is that it could manipulated to make conquering a massive swath of Western Europe much more feasible.
Right. What about implementing actual titles based on real historic territories?
For example:
Charles V was "Archduke of Austria", "King of Spain", "King of Naples & Sicily", "Duke of Burgundy", "Count of Flanders", "Count of Holland", and "Holy Roman Emperor".
Philip II was "King of Spain", "King of Portugal", "King of Naples & Sicily", "Duke of Burgundy", "Duke of Milan"
Leopold I was "Archduke of Austria", "King of Bohemia", "King of Hungary", "Duke of Burgundy", and "Holy Roman Emperor"
George III was "King of Great Britain & Ireland", and "Duke of Hanover"
This would mean many more possible titles, all based on amounts of provinces ranging from just 1 (Milan) to more than 10 (Great Britain & Ireland). I was thinking we could have the bonuses vary accordingly. For example, being only the Duke of Milan would give a small amount of culture of science, where being King of Spain would give a larger amount of faith points, etc. Being both gives both obviously, so this a fun to way to go around collecting titles. Smaller civs can participate this way, and there's no limit to what creative bonuses we can think of for each title.
The titles are going to overlap somewhat, but we can make smaller titles go away when conditions for a larger one are met. For example, the ruler of the English provinces is King of England until all of the Scottish provinces are captured, then its the King of Great Britain, providing a greater version of the England bonus. Conquer Ireland, and you're the King of Great Britain & Ireland, which gives a slightly better bonus still.
There's some kind of real, historic title for the core spawning area of every civ in the game. Muslim civs would get "Sultan/Khan" for "Emperor", "Caliph" for "King", "Emir" for "Duke/Prince". Orthodox get "Tsar" for "King" and "Emperor", rest stay the same. Every civ with a monarchy would start out with some modest title and get the chance to work their way up. Civs with Merchant Republics get excluded. At the founding of their first city:
France: King of France (The Franks? Changes after spawn of Burgundy?)
Lombardy: Duke of Milan
Arabia: Caliph of Arabia
Bulgaria: Tsar of Bulgaria
Cordoba: Caliph of Cordoba
Venice: (merchant republic)
Burgundy: Duke of Burgundy
Germany: (Won't discuss, since we don't know if there will be a Germany civ)
Novgorod: (merchant republic)
Norway: King of Norway
Kievan Rus: Prince of Kiev
Hungary: King of Hungary
Spain: King of Leon
Denmark: King of Denmark
Scotland: King of Scotland
Poland: (Grand) Duke of Poland
Egypt: Sultan of Egypt
Genoa (merchant republic)
Morocco: Caliph of Morocco
England: King of England
Rum: Sultan of Rum
Bohemia: King of Bohemia
Portugal: King of Portugal
Aragon: King of Aragon
Serbia: Prince of Serbia
Sweden: King of Sweden
Prussia: Duke of Prussia
Tunisia: Caliph of Ifriqiya (Tunis)
Lithuania: (Grand) Duke of Lithuania
Austria: Archduke of Austria
Turkey: Caliph of Turkey
Muscovy: (Grand) Duke of Muscovy
Crimea: Khan of Crimea
Netherlands: (Republic)
Prussia, Poland, will of course become Kingdoms after expansion into other provinces, Turkey becomes Sultanate after expansion. I'm not against the idea of the large "Rex Britannia, etc." titles, but these are historic titles and I suggest that its more fun to make small titles with small bonuses available to small civs.