I've said before, to give us both a larger variety of basic Civ types and cover historically important and interesting groups that the game has not modeled well in the past, I think the game needs two things:
1. A decent model for the City State polities that at least makes them competitive - and given the modern examples of 'city-states' like Singapore and Dubai there's no reason they can't actually strive for certain types of Victory Conditions right to End of Game.
2. A model for the pastoral nomadic groups that dominated central Asia for almost 2500 years and had a huge impact on their Civ-normal settled neighbors.
For discussion, let's take the pastoral groups that
@Bonyduck Campersang's Hun model depicts.
To start with, they were not all completely Non-City-Building (or 'acquiring'). While Attila's European Huns collapsed as soon as Big A bit the dust, other longer-established Hun groups like the Hephthalites and Kidarites, and other pastoral groups like the Scythians, Avars, Magyars, Kushans, and Mongols either turned other people's cities into vassals, or made them into their own, or founded a few: cities were never the sources of their military power, but many were real manufacturing hubs and major trade nodes for them.
Second, they were not Technological backwaters for most of those 2500 years. We are now pretty sure that a number of very important tech advances originated with the steppe pastorals, like the spoked wheel chariot for certain and the composite bow and 4-wheeled cart with front-axle steering mechanisms as possibilities. The sophisticated lost-wax casting technique seems to appear in central Asia before anywhere else, also, which would be surprising if we didn't also know that the early pastorals were sources for minerals they exploited in their territories and traded to settled neighbors.
Third, and possibly most important to their difference from settled states, the source of their military power was not from any cities, but from the lifestyle of their mounted herding population, scattered about in smaller tribal/clan/family camps. Virtually all of the adults in these camps were mounted archers, a military type very difficult for any settled state to produce in numbers because of the time and space required to raise horses, train them and train numbers of men (and women) in both horsemanship and mounted archery. Quite simply, you cannot do any of this on a large scale in a city, and as the Tang Chinese discovered, setting aside large tracts of land to feed horses means it is not feeding your peasant farmers - and they resent that to the point of rebellion.
Now, I've already suggested revamping the Barbarian Camp/Tribal Hut system into uniform Settlements, and allowing Civs to create smaller-than-city Settlements to exploit Resources or provide Trading Posts to extend land trade routes. This also provides a ready-made model for the Pastoral Camps.
The difference between 'regular' and Pastoral Settlements, I suggest, might be:
Regular Settlements can work/improve 1 tile adjacent to the tile the Settlement is on. Pastorals, being more mobile, can work 1 adjacent tile plus any tile with an Animal Resource within 2 tiles of the Settlement tile. (This 'wider range' also reflects implicitly the mobility of the pastoral wagon-based camps without having to physically move them around the map, which would be Micromanagement at its Worst). The single adjacent Improvement and 1 Animal Resource Improvement are Free and may be automatically placed with the Settlement. Improving more Animal or other Resources around the Settlement requires a Worker, just as City Improvements do.
Each Pastoral Settlement can produce 1 Mounted Archer (or the Unique Unit for the pastoral group). Any other type of unit must be produced in Cities or hired from outside groups, like city states, friendly foreign Settlements, or even Civs (Note that Dacians fought for the European Huns and the Mongols later had both Chinese and Persians fighting for them as infantry, siege artillery, and other 'specialists')
A Pastoral Settlement can be placed on a tile by any Pastoral Settler. It takes a second Settler to turn a Pastoral Settlement into a City - but Pastoral Settlers cost about half what 'regular' Settlers do. Pastoral Settlements, like regular Settlements, cannot produce or support Districts other than certain types like Holy Sites. They can support certain Wonders, but only those specified as being Non-Urban (Stonehenge, Pyramids, etc)
Pastoral Workers are required to Improve tiles for a city, and are produced in a City or from captures (see below).
Any 'foreign' Settlement or City captured by a Pastoral combat unit produces a Pastoral Settler OR Worker as the pastoral player desires. This destroys the other Settlement, but not necessarily the City.
Pastoral land Trade Routes have increased Range compared to regular land trade routes. Pastorals can also Trade Resources they obtain from a third party - literally acting as 'middlemen' between two other Civs or City States.
Pastoral Settlements, depending on the resources they are exploiting, can produce Science, Production, Food, Religion just as regular Cities can, but normally in smaller amounts.
Obviously, in addition to this 'basic Pastoral Framework', Unique attributes and units could be added for specific Pastoral Civilizations like Attila's Huns, Genghis' Mongols, and a host of other potential groups between the Hungarian plain and Mongolia.
Just initial thoughts, but it might provide the beginning of a framework for modeling the pastoral nomads, and by not making them completely Non-City-Building also provides for their transition to 'regular' Civilization that will be required for them to survive longer than the great Pastoral Empires did.
Just a note, though: several of the 'standard' Civilizations in the game started out as Pastoral Groups and graduated to 'regular' civs relatively early: Persians, Ottomans, Mongols for three that spring to mind . . .
