I like the idea, but perhaps it shouldn't be a simple progression. We would need to figure out what citizens add to the empire and design different types based on that. Some ideas could include...
Craftsmen increase production and taxes, neutral on research, and weak on political influence and cultural influence.
Enlightened Folk increase research and cultural influence, neutral on taxes and politics, but don't add to production as much.
Statesmen increase political influence and cultural influence, neutral on taxes, but don't add to production or research as much.
Artisans increase cultural influence and taxes, neutral production, weak on politics and research.
If there's religion, Clergy add to cultural and reduce unrest, but don't add taxes or production.
Laborers only add base amounts to production and taxes and nothing else, but can be trained as something else, but while being trained they add nothing.
Slaves add to just production, but don't count to unrest, unless the town rebels. Can be freed to become Laborers, but unless there's a job for them, and a place for them to stay, they will raise the unrest.