Something I loved about Endless Legend was the rich collection of "Minor Factions", each of which had distinct character and mechanical benefits.  Certain minor factions were great to complement your military (in EL, each major faction has gaps in their army, and assimilated factions can bring archers or defenders if you have none); and their empire bonuses, while following the same mechanical pattern, added variety to each playthrough and made each newly discovered territory a surprise and a possible treasure.

The Independent Peoples in Humankind are mostly all the same as one another, except for being "Peaceful" or "Hostile".  While the Metternich update has given us interesting new mechanics to interact with them, they still remain a city to absorb or to sometimes-too-easily conquer, and each one is the same.  We prize them for their land and not for their distinctness or flavour.

When Humankind launched, all Natural Wonders were the same too, and but they've all been given neat new benefits.  Some are stronger than others (which is fine) but they're all unique and they challenge us to build a city that works with them.  Following that same philosophy, Independent Peoples can be the same.  We can be excited to run into Nok and dread Avaris, and seek to court Tlatilco for its unique benefits even though it is on the border of our rivals. 

Proposal: Just as Natural Wonders were given varied and interesting benefits well after the launch of Humankind, Independent Peoples should be given benefits to empires that appease them diplomatically with the "Client State" or "Assimilate" treaties (possibly with/without combination of Civics).

Each IP could give a unique "Cultural Mosaic Trait" to a major empire, a trait that can only be gained through peaceful means and would be lost if you captured the city.  Upon making an IP a Client State or assimilating them, we could be treated to a new pop-up: "The people of Huaricanga have been welcomed into your empire with open arms!  As they mingle with your population, they bring with them their arts, their ideals, and their secrets."

These don't need to be major boons — just enough to make each independent culture feel different and to be worthwhile enough to encourage us to interact with them peacefully instead of conquering them.

Some examples for "Cultural Mosaic Traits" could be:

• +2 Faith on Farmers Quarters
• +1 movement on Ranged and Gunner units
• +3 influence on Artisans Quarters (Luxury districts)
• +2 money on empire per researched technologies
• +2 science on territories influenced by your state religion
• +5 or +10 food on harbours
• +1 movement on Naval Units
• +25% Fame on Merchant Stars
• -20% Production cost on Cavalry units
• +100% faster outpost creation

Additionally, a handful of IPs could even have their own unique luxuries to buy from, to make them more interesting; Nok terracotta, for example.

Additionally and finally, independent peoples could have slight differences in the way they exist as Independent People (but with far less variety), favouring spearmen or archers, favouring one district over another, or being cheaper or more expensive to bribe with money or influence, or sending their armies far and wide or remaining isolationist and patroling only their borders.

+1
I would really like to see IPs finally get some character depth. Finger crossed for the next update.