Could go with Parthia or Seleucia (Seleucid Empire), Sassanids (Sassanid Empire) or Kush (Asian Kush).
Lots of choices aren't on the voting list.
For example:
Khazaria
Prussia
Parthia
Belgium
Comanche
Etruscans
Papal State (Vatican)
Crusader State - never going to happen but we could see if anyone would vote for them
Wends - west slavic tribes (now almost all vanished), led by Samo for example
Finland
Lithuania - was a large pagan state for quite sometime
Numidia
Libya
Media
Elam
and a few more
7 votes isn't enough, I'm afraid.
- Parthia and Sassanida are simply part of Persian (Iranian) civilisation, culture and heritage (same as Tang is period of Chinese history). I know that civ series always portait "Persia" as 100% Acharmenids but that's their mistake I'm irritated by. Personally I wouldn't mind pan-dynastic Persia with elements from various dynasties, or alternate leaders from various dynasties. Hey, that's the exact thing always happening with European civs - such as Barbarossa with Uboot and Jadwiga with Winged Hussars.
- Prussia is, similarly to Parthian case, considered to be part of German civilization. In several civ games Frederick was the leader of "Germany" and I'd support him... as alternate leader of it.
- Etruscans are in the poll as Etruria

- Comanche are, I presume, part of "Apache, Navajo etc" option as Plains Indians - alternately you could say they already were in civ, as hybrid with Shoshone (it literally had comanche as unique unit)
- Belgium is unlikely imo. It is very recent, very artificial construct consisting of two separate cultures that barely can coexist under one state. On top of that, the only "spectacular" thing Belgium did during its existence was... genociding Kongo. Yeah you could say "but Belgium has much economy and culture" - and the same about almost every European country today.
- Vatican is one of the most city-state civs ever

- Wends and state of Samo are completely separate thing lol.
- The only significant thing Finland did was Winter War and its postindustrial era prosperity
- Media lasted for a short time before being completely consumed and eclipsed by Achaemenids

- Numidia and Elam didn't really manage to be particularly spectacular, unique, or achieve much during their time
- Has concept of a united Libya ever been a thing before being created as Italian colony?...
However!
I support Khazaria and Lithuania,as well as Prussia and Parthia but only as alternate leaders
IMO missing civs are Mexico, Switzerland, Yemen, Afghanistan, Nepal, Tamils/Chola/Sri Lanka, Bengal, precolonial Philippines, Maori, Bactria/Sogdia/Kushans and Malagasy.
Also Somalia, Hausa, Yoruba and Igbo but I am afraid only me would vote for them
