So, I was wondering how the eras would work and thought about the following:
I am unaware of the number of eras you wish to add so I'll suppose that you would add those bellow:
The stone age would work as you already have it, by creating a small civilization with the first glimpses of organized faith.
Medieval goes further by having the clergy consolidate power and faith being a huge deal, holy wars happen, e.t.c. You can interact with the religious figures and use them to spread religion and reform society. Also the first power structures in society form and you can start taxing nuggets.
Enlightenment would be where tech starts to gain significant traction and people starting to question the authority of the church ( reformations, inquisitions, tolerance towards different religions or civil unrest, e.t.c.).
Industrial era is where you start the efficiency vs echo friendlyness dilemma. It would be fun to see different political ideologies being represented and people fighting over them. The working class would want more rights and to form unions, which would decrease productivity but increase happiness. Jingoists would want to expand and have a society ruled by the military (unrest reduction, better fighters as well as less happiness), the monarchy would cling to power and try to keep the status quo, the democrats strive for tolerance, hell you could even add zealots wanting to put the church in control of society and advocating for religious persecutions). You could add more political ideologies this way and have the system be quite organic and add to the replayability.
Modern era is equivalent to 1930 - 50 years from now, pollutions choices here and the wish for self sustainability and survival. Civs develop wmds, large scale wars can happen with the possibility for nuclear annihilation. Civs try explore/escape to the stars and start building the first space exploration modules.
Future era would be the age of space colonization, teleportation, more cyberpunk.
Now all that is well and good, but what about adding one more era, the devestation era? Let me explain:
When civs reach the modern era and onwards, large scale wars and catastrophies can happen that could result in the utter devestation of the nugget race. Thus the civs would reach the devestation age (think Fallout) which would be a transition period from the current age to a previous age. Throughout this transition the player would try to undo the damage he did and try to have his civ hold it together. Perhaps he could lose some epicenters and have them declare independence. Perhaps the more time passes, more and more unrest is generated and more and more epicenters declare independence. If enough time passes, the player will be left with one epicenter and have to play from the stone age. If he rectifies some of his wrongdoings, he will not go as further back as he would otherwise. If the player is completely successful in his endeavours, he might go one era back of even stay to the one he was previously. This whole process adds to the replayability and helping solve the problem that finite technologies cause. By going back, you forget tech and basically have to reinvent the wheel (sometimes in the literal sense).
Here is a post I made regarding faith which explains some faith related points better.
What are your thoughts people and devs? (Devs are not people, devs are gods that try to make this masterpiece happen )