Here's a status update for currently and as of yet not currently planned civs:
Lithuania: Next Major Update
Golden Horde: Following Lithuania
Pueblo: Eventually. I'm going to need to make a model for their UB as the one that I did was rather underwhelming and didn't really give a good idea of what kind of structure it was.
Sogdia: Currently not planned. I am concerned about how they'll impact the Yuezhi's chances at conquest, though as a counter to that, they might make the Yuezhi early game more consistent by warding off Persian conquests of the region in favour of capitulation/vassalization. At the same time, that means they'll have to start with enough units that they could feasibly defend against the Yuezhi conquerors, which is itself a bit of an issue. In summation, unless there's some periods in which a resurrection would make sense, I'm not sure their existence as an AI would be long enough to truly warrant being added.
Scythians: Probably not for all the reasons previously described by other people.
Assyria: Following Big Map's Addition
Armenia, Hittites: I'll consider them following Big Map's Addition
Scotland, Chile, Peru: Following Scrolling Scoreboard's Addition (I really need to get back to trying to figure out the code for that)
Iraq, Bolivia: Maybe, same requirement as Scotland.
Maori: Would be interesting to have a nation to interact with the Polynesians, especially since their AI is now in game and pretty consistently explores and settles New Zealand due to the tile they spawn on. While I have other priorities before them, I absolutely plan on adding them eventually.
Goths: Eventually. I've been wanting to also rework France's early game so they'll probably come in the same update.
North Deccans and Maratha: Eventually.
Haiti: Still on the fence for this.
Songhai, Zulu: Probably not. Their historical time span and territory, respectively, are very small.
Also, new small, long overdue update.
Arabia no longer erroneously starts by being led by Saladin, now stars with Harun
Mamluks no longer erroneously starts by being led by Baibars, now starts with Saladin
This has been out for the last hour but I was spending time with family so I have only now been able to complete this post to announce it and my plans. Yes, I did go through every single page of this thread to gather all the suggestions. If I missed anything, please let me know.
I suggest the Uyghur people as a possible respawn of the Sogdians. I imagined this because both peoples are closely linked, and I can say that the Uyghur people are the successors of the Sogdians in the Tarim Basin, especially in relations with China. Another suggestion that I would point out would be the Khitans, especially in the figure of the Qara Khitai, since they inhabited the same spaces in their final migration. Both the Uyghur and the Khitans would be a good option as a challenge for the Chinese, Turkish and Mongol conquest, relegating the Sogdians to Antiquity and the Dark Ages.
Proposal for New Civ: Uyghur Khaganate
Leader: Bayanchur Qaghan
Starting Religion: Tengrism or Manicheism (it can be represented by zoroastrism).
Spawn: 657AD (the last sogdians Kingdom fell in 673-751 AD, this date is the date of the split betwen uyghurs and Turks at a battle wich the Uyghurs defected to the Tang) in Ötuken or Karabalghasun.
UP: Uyghur Alphabet: double production of library and universities and dont recieve penalites by change your capital in a region wich is not your core province.
UU: Uyghur-Sogdian Diplomat: replaces a spy, when put in a city wich have open borders treaty with you, the cits owner recieves a boost relations with you and +1 research, and you recieve a small amount of gold (like a friendly pirate), maximum 1 unit per city.
UB: Translation House: a library wich gives +1 happiness with each religion in this city and give +1 trade routes. The Uyghurs inherited the Sogdian tradition of translating vast religious works and commercial treaties throughout Transoxiana and the Tarim Basin.
UHV1: The Ashina Clan must die- Take 3 Turkish cities, one of them must be their capital.
OR Raze a Turkish capital. The uyghurs destroyed the second göktürk khaganate and take their capital.
UHV2: Together with An Lushan or the Tang Empire - Capture a Chinese Capital, and make it your capital and control another 3 cities or have friendly relations and ensure 1 silk and 1000 gold by tributes with China by 1209AD.
UHV3: Successor uyghurs kingdoms. - Control and spread your state religion to all Transoxiana, Tarim base and Gansu province and esure control 3 Cathedrals type building of any kind in 1100AD.
Proposal for New Civ: Great Liao/ Khitan khaganate.
Leader: Abaoji
Starting Religion: Tengrism.
Spawn: 916 AD in inner Mongolia.
UP: Great Liao heirs: Start with meritocracy and +2 stability by each controled chinese cities.
UU: Khitan riders: replace Horse archer, start with city raider III and mobility.
UB: Five circuits: courthouse, avaliable with Education, gives +1 Happiness and -50% maintenance.
UHV1: The Great Liao- Control Mongolia, Manchuria, Tarim base ,Transoxiana, Korea and build 5 courthouse in 1000 AD.
UHV2: The tales of Cathay- Control all China, build a capital in the former Chinses empire and be the wealthiest nation in world in 1100
UHV3: The Qara Khitai - Ensure there no turks in Transoxiana and Iran and build 2 buddhist Chaitya and 2 Orthodoxy Cathedral in there by 1125AD