Some quick ideas for features that are underdeveloped or non existent in humankind

1 Energy

Right now electricity plays a small, almost insignificant role in late game. You get 50 fame for discoverying it first and you get access to some infrastructure that boost your industry, but that you can easily live without. 

My idea is to introduce the resource "energy". Each pop in cities consumes or needs 1 energy. How you provide it to them? By building power plants: theese are not infrastructures but quarters, that you build and see on the map. Each plant produce energy, lets say 30 energy for a coal plant, 50 for oil, 150 for nuclear, 20 for green.

All pop that have access to energy produce FIMS regularly, pop not provided with it has severe malus in production.

On the other hand power plants pollute (i'll be back on this), also coal and oil plants gives malus to adjacent tiles, while nuclear plants may explode.

This creates a tension, progress vs ecology, economy vs quality of life, something that we experience in everyday life: I need 100 energy, but i don't want to waste time in building 5 solar plants, 2 oil plants will do. But then on the long run I'll get malus for pollution, so what do I choose?

You can also add infrastructures that lower the energy consume of pop, let's say energy consume reduced from 1 to 0.66 per pop. You can expand this concept as much as you want. 

Elecricity is what made industrial era so unique, in civ 6 energy management is one of the few things I like form that game, while humankind basically forgot about it

2 Pollution

First things first: remove this thing where I can end the world by building a couple of train stations and airports. It's rediculous.

Now that I got that off my chest: pollution should effect population. I mean, ok the stability malus, but pollution kills people. Introduce some narrative events where due to high pollution people dies, or an event that make you choose between destroying an obsolete coal plant and reduce your pop by 30. Harsh food malus should be introduced.

Off course, pollution works with time: you pollute the world of your grandchildren, and everithing is fine unless you are the grandchildren. So in industrial age you are basically free to pollute as much you want, but then you (and your neighbors) will have clean up the mess the next era.

An impact on the map like in civ 6 would be nice.

Also top polluter, instead of being rewarded with fame (seriously guys), should get fame malus, like fame stars worth reduce by 20% or something like this.

So like this you need to be careful, your economy may be great but you need to balance it or you might loose pop, fame, the game eventualy. Right now, if you're firts fame wise, you burn down the planet so you can be the king of the ashes

3 Religion

Coming from an atheist: give to the spiritual expirience in Humankind a respectful representation.

I can be a zoroastrian today, a christian tomorrow, and a buddhist the day after. All that change is just the look of my holy sites.

Treat religions as cultures. They unlock with eras: you start with polytheism or shamanism, then you can choose judaism, zoroastrism buddism, after that you got christianity and islam later on.

Each religion gives different legacy bonuses (jews are harder to convert, muslims has bonus in conversions, christians can spend money to generate faith, and so on). Every time you keep your previous religion, the bonuses get stronger. You can choose only available religions, just as you do with cultures.

The cherry on top? each religion has dedicated narrative events, like the schism for the christians, and depending on your choice you get to be orthodox, catholic, nestorian, all with different implications. 

Religion should give fame as well: I'm not saying religious stars (which could be a thing), but a fame reward everytime a religion reach a certain followers number.

With atheism ,you can destroy other people religion and their bonuses (basically is a religion that attacks all the others), while with secularism you're out of the game, but followers of foreign religion in your territories won't count for the other empire's fame reward.

The grievancies system is fine the way it is.

Like this investing in faith rather than science in ideology could be interesting, an faith in late game could still be relevant.

Thanks for reading so far, let me know what you guys think.

PS: the numbers that I provided are just for examples, in game numbers need months of testing and balancing, this is just a post in the forum