[LDiCesare]

Adding national spells based on how the game evolves could be fun:
1st to reach level X in research unlocks national spell Summon Nasty Djinn.
Whoever controls DeadRat Province unlocks unlocks national spell Summon RatLord.
Nation controlling least number of provinces, and, if tied, best in research, by turn 12 unlocks Summon Meek Paladin.
etc.

Longer to code, nation specific events could be done too, like:
Any nation controlling less than 12 provinces by turn 10 and the 2 smallest nations (more if tied) by turn 10 get a permanent discount of 10% in gold and +1 attack for their best non commander unit.
Nation with best dominion by turn 15 gets its weakest national priest gain H2 if it was only H1, with a cost increase of +20 gold.