Many 4X games feature factions built around "wide empires" (lots of average cities) vs. "tall empires" (having fewer cities but more potent ones).  Amplitudes' own Endless Legend and Endless Space franchises pushed these in extreme (and well-balanced and playable!) directions with the Cultists, Mykara, Allayi, Umbral Choir, Cravers, and more, where the playstyle didn't focus on building a moderate amount of balanced cities/systems.

Humankind has to be different in this regard, since your culture and traits change over the course of the game, but there's still potential to have cultures whose traits tip you towards wide vs. tall empires.  Most obviously, I think, the Achaemenid Persians +2 City Cap sets you up early on for a wider empire than anyone else.  What abilities might we see from new cultures (or new Civics or Tenets) that could boost a tall or wide empire?

The challenge of "Tall" traits, of course, is to come up with benefits that don't also benefit wide empires. Most 4Xs do this with faction-specific penalties on "tall factions" to discourage sprawl. Humankind absolutely shouldn't work this way, and would require "tall" benefits that only activate with a small number of cities, or that simply don't benefit building too many.

Tall Empire Possibilities

- +X (30-60?) Stability on your # largest/earliest cities.

- A significant "Attach Outpost" discount (more than the Mauryans) to encourage fewer, larger cities

- Reduce the stability penalty for attached territories from -20 to -10  (In a way, the Ming do this already with their Grand Teahouse) to encourage fewer cities to fill the same amount of territory

- FIMS% improvement (+10%, +20%, maybe +25%?) as long as your city count remains low.

- Benefits to Liberating your cities into Independent Peoples

Wide Empire Possibilities

- City Cap increase (already present with the Achaemenid Persians)

- Flat stability bonus on cities (also A.P.)

- Movement benefits within own territory to encourage spread and control

- Influence cost discounts founding distant outposts and/or influence cost discounts on converting outposts to cities.  (Bantu already have a sort of influence-free outpost, which is neat!)

- Late-era (IV+) garrison-EQs that can be built in outposts — like the Dunnu — for claiming and defending wide areas of territory into the later game

SudoPotato wrote:
The current district cost formula balances many small cities (few territories) with more districts versus few large cities with fewer districts, yet better utilisation of infrastructure.

This is a very healthy thought! IMO the core of city building and development is solid now. The only thing about cities with lots of territories is defensive infrastructure. Garrisons become super costly with all those territories attached and defence of your far borders can become very difficult. I'd like to see a trait unlocked by technology that gives +1/+2 CS around administrative centre. There is already that kind of tech for the outposts.