Okay, so here will be an unusual opinion: Kenya or Tanzania are better civ candidate than "Kilwa - Swahili" in every way.
0) So what if they are comparably very poor for global standards nowadays. They are iconic and very important for modern Africa. Zulu and Shoshone look much worse in comparision to other 19th century civilizations
but nobody had problem with that. It would be also nice to trash this awful stereotype that modern Africa is only a humanitarian crisis and nothing more.
1) Countries themselves (colonies) are very young, but cultures they cover are centuries old, and their areas contained civilizations two millenia ago already (though local archeology is obviously in its cradle yet). So no 'wah too young' argument, they definitely have more of a 'civilization' feel than Australia and Canada anyway.
Besides, I'm damn sure we have several civs in series which existed for less than 60 - 120 years.
2) People always talk about Swahili as some sort of awesome repredentation of East Africa, but it covered just coastal areas. Simply adding Kenya to the game would obviously represent peoples of Kenya better than either Swahili coastal strip or choosing random one of its count less nations (such as Masaai who amount to 2% of Kenya lol).
3) Kenya or Tanzania would also simultaneously represent civilizations of African Great Lakes.
4) Both countries are cool, their cultures are cool and Kenya is among few most respected countries of Africa (next to Ghana).
5) Both civs would include Swahili language, culture and cities anyway. Mombasa and Zanzibar would be literally second cities on Kenyan or Tanzanian city lists.
6) Both civs have awesome, charismatic founding fathers who are mostly beloved by them and respected by the world, so in this regard they immediately crush the endless issue of 'faceless' Kilwa (civ5 mod was so desperate it went for barely historical Persian dude and made his tan look kinda black
)
7) Both civs obviously have HELLA lot more of documentation to take inspiration from than still poorly researched Kilwa.
8) They have very peaceful and wholesome history for post-colonial African standards (compare with Biafra and Derg) and they are both among most peaceful African countries with best economicc prospects, while also being big, so it's not like they feel awkward due to being quite insignificant or in disastrous shape (Sahel states, DR Congo).
9) And this point is the most important one, Kenya or Tanzania would genuinely offer much more content for gameplay purpose than Swahilli/Kilwa.
Have you ever realized how goddamn boring all actual gameplay concepts for Kilwa look? It is always purely 100% "city coastal navy trade civ" with dhow trade ship and coral port or mosque or whatever, it is one dimensional design u less we know much more of those people. With Kenya or Tanzania you can go crazy and go for their culture, tourism, money, agriculture, diplomatic successes, UN missions, unique ideologies, legacy of countless cultures, Masaai, their ww2 military units or modern (UN missions) military units or special forces, or precolonial resistance units, and you can even go for "Indian Ocean trade" naval stuff just as well.
10) We have plenty of candidates for precolonial Sub-Saharan civs, well what about post-colonial one.
Tl;dr Kenya or Tanzania are better civ candidate than "Kilwa - Swahili" in every way.