I think there is one problem we all player would feel. The hardest part of the game is at the beginning until having few territories (Castle or City) and supporters, which also the best time of the game. After we have lands and vassals there would only the same things to do and it just time to end the game. It started become boring. Therefore, it is the hard part in how to keep the game continue.

I suggest to let the Kings return like become commoners after kingdom is defeated, but keep upgrading themselves to come back and rebuild their kingdom.

- All vassals may have chances to have whole top tier army (specially after player build their own kingdom) instead of having recruits or middle class troops.

- Some vassals may try to rebel players kingdom. Martial like players may turn peace vassals rebel and wars like lord will rebel peaceful players. Also events like big rebel (selfish lords lead commoners and farmers to rebel the kingdom) can add in the game

May be that can increase the level and difficulties for player to role the whole world, but also more interesting for players. I don't know if these are good suggestions, but I would like it.