99 for Civics and no more than 6 for anything else isn't enough?
The long-term timing thing is interesting, but maybe unrealistic. Countries can certainly fall into an effective police state quickly, or a theocracy, etc. However, shifting out of a labor civic could realistically take 100 turns. So maybe different categories should have different timings.
While I think the civics work well as a gameplay system (as in, even when you have ALL civics, there are at least 2, often 3, valid choices in each category), they were clearly not very well thought out historically. As already noted, slavery is not incompatible with anything in that category, including emancipation! How do you deal with a country like the US, where a small portion of the country was enslaved, and the rest were free labor? Isn't there also a difference between free labor in 1890's US and modern Scandinavia or Germany? What civics does China run right now, State Prop? Free Market? Emancipation? Certainly not ANYTHING from the religion category!
So I like the idea of at least a new set. However, you have important decisions to make if you increase the number of them. The more civics, the more powerful spiritual becomes, because the incentive to change will be higher. Also you increase the likelihood that some civics will be indisputably better than others, because there are really only so many ways to play the game (because there are only 4 ways to win!). At the very least they should think really hard about all the different ways you can organize a society's, say, labor, and figure it out. Maybe adding another category makes more sense than expanding the list beyond 5.
Just one more thought... you could also have the civics make a much bigger difference than their current relatively passive effects. For instance, if you are running slavery, you could have your citizens divided into "slave" and "free" labor. They could have different abilities, like free labor is more productive, but slave labor somehow "costs" less. Actually I REALLY like this idea, you could also have different levels of education/training and what not...