Edit: The following was written before civics were announced:

I liked the influence and laws system that Endless Space 2 had, but the fact that all laws required upkeep rather than some being permanent unlocks seemed odd. I think Humankind could use a system like it but expanded to great effect. You could have a tab which has a list of available policies and reformations which you can enact, usually at the cost of influence, but sometimes at the cost of gold or temporary production disruption.

There can be a few kinds of reforms and policies. Some are inevitable so if you don't get it by the end of the era you get it automatically, while others stay until you get them, and a few might be missable. Some are simple reforms you enact to unlock a permanent bonus, while others are a policy you can switch between two options. Some might be repeatable actions such as propaganda which would allow you to spend gold to buy influence. Some cultures might have a unique reform or get a reform early.

Additionally some reformations can have a public impatience counter. The longer you go without them the more upset the public is leading to protests, rebels, and finally a civil war if you delay too long. Some, for example abolition of slavery, might have worse rebels and if you apply it too late you might get a civil war anyway.

I did a bit of research and found that the history of law reform is very complicated and I was surprised to find that a lot of seemingly simple laws and taxes are more recent than I realized. I definitely don't have the expertise in history necessary to list an accurate history of reforms, but below are some simple examples:

Ancient Era
Perform Jubilee (debt cancellation)
Land owning regulations
Code of law
Ban bribery
Implement district-based representation
Corvée vs Tithe tax (labor vs money)

Classical Era

Family reform (tax unmarried and childless, ban adultery, stricten divorce)
Implement advanced taxes (sales, import and land tax, public taxmen etc)
Standardize coinage
Establish elite guard
Democracy

Medieval Era
Feudalism
Civil service system
Caste system
Religious corruption reform (ban simony/indulgences)
Perform patronage
Ban heresy

Early Modern Era
Constitution

Bill of rights

Mercantilism vs free market
Implement corporate law
Religious reformation
Equality before the law

Industrial Era

Labor rights (child labor, 8 hour day, anti-trust etc)

Universal Suffrage

Basic women's rights

Abolish slavery

Public education

Judicial reform

Communism

Merit System vs Spoil System

Propaganda

Contemporary Era

Full women's rights
Racial equality

Sexual liberation
Environmentalism

Progressive Taxation

Deficit Spending

Religious fundamentalism vs secular progressivism (gay marriage, abortion, etc)
Public Elections

The civics tab that Amplitude has announced clearly takes the place of my original idea. It looks pretty good, but the civics which have been shown were all a this-or-that choice. Some should be controversial decisions, but others I think should still take the form of reformations which are simply unlocked. Some policies such as standardized coinage don't really have an alternative other than just not doing that. I also hope that some of them can be changed later on at a cost.