I think this would be way to much. I mean... how many cadet branches would the Karolingian dynasty have with this mechanics if EVERY son get's a own cadet branch?
And if it's only affect Children without any inheritance:
How would Capet cadet dynasties work? The cadet dynasties of the Capetian dynasty were all landed.
How about creating cadet dynasties when landed male dynasty members leave the realm of the main dynasty?
I realize that's a fairly vague standard, but you could implement it using some simple rules.
When a liege changes, the game calls a function as follows:
- Was the old liege from the same dynasty as the vassal?
----> No: no effect, return.
----> Yes: is the new liege from the same dynasty as the vassal?
------------------> Yes: no effect, return.
------------------> No: create a cadet branch for the vassal and his (matrilineal: her) descendants.
When an adventurer wins a war, the game calls a function as follows:
- Does the adventurer become a vassal?
----> Yes: is the new liege from the same dynasty as the adventurer?
------------------> Yes: no effect, return.
------------------> No: create a cadet branch for the adventurer and his (matrilineal: her) descendants.
----> No: was the loser in this war from the same dynasty as the adventurer?
------------------> Yes: no effect, return.
------------------> No: create a cadet branch for the adventurer and his (matrilineal: her) descendants.
So the Duke of Brittany's cousin somehow ends up ruling Crete, they're going to be in a cadet branch. On the other hand, landing his second son in Rennes won't create a cadet branch - unless the King of France/Emperor of Francia conquers the territory from the Duke, in which case the House of Brittany-Rennes will set off on their new destiny, but still with an opinion bonus to their siblings->cousins->kinfolk over the border.