I think, it's good idea to make special events for growing power of different classes.
For example, i built court, brewery or other economical structures(its meaning that economical power of towns are growing) . So i have a chance that happens event in that power of burghers are grown up.
If i built castle, palace or other structure for nobles, then power of nobles can grow.
And so on for clerics(churches, cathedrals) and may be peasants(fishing wharf, forestry) but in smaller scale
Then during the game as AI and player advance their cities, the power of burghers and nobles power will rise and power of peasants will fall, as it was in real history.
For example, i built court, brewery or other economical structures(its meaning that economical power of towns are growing) . So i have a chance that happens event in that power of burghers are grown up.
If i built castle, palace or other structure for nobles, then power of nobles can grow.
And so on for clerics(churches, cathedrals) and may be peasants(fishing wharf, forestry) but in smaller scale
Then during the game as AI and player advance their cities, the power of burghers and nobles power will rise and power of peasants will fall, as it was in real history.