Well I'm sorry if the tone of my last post was offensive.
I just think it's pretty clear that not all historical civs have an equal chance of being represented in game, and it has a lot to do with their historical relevance (among other things).
So like, there are major civs like Egypt and China that pretty much everyone has heard of, that are almost certainly going to be in game. We already have most of that category but we're missing a few, still, Mongolia, the Ottomans, Korea, the Inca, maybe a few others. Then there are influential civs, that aren't really common household names but that legitimately had a major impact on human history. Most of the civs in the game, especially in DLC, are in this category, and for the most part I think the new African and SEA civs are likely to be this type, civs like Mali and Ethiopia and Siam/Thailand and Vietnam.
Then there are minor civs, that were very short-lived or had only a regional impact at most, and didn't really play a big part in shaping the course of human events, and aren't usually that well known among players. In some cases they still end up in the game, like Australia, or like some people have speculated some sort of Philippines civ, for other reasons - like having a lot of Civ fans in that country. But when there isn't any particular reason to include them, I think it's very unlikely that they'd end up in the game - civs like Madagascar or Brunei, for instance, very few people have heard of them mostly because they had little to no influence outside their region.
And yeah, I know there's a whole political correctness thing with colonial Western influence but the fact is, civs that embraced contact with other cultures and have an extensive colonial history generally played a bigger role in history than those that remained closed off and rejected outside influence - history is, after all, about different nations and cultures interacting with each other.
As far as Singapore, like, it's the most literal example of a city-state in today's world, it just makes no sense to include a mechanic like city-states in game and then represent what is obviously a city-state as an entire civilization, especially when there are city-states that represent civilizations. I think it's much more likely we get Singapore in the same patch as the SEA civ as a commercial CS.
Idk, I know I've given a very simplistic view of things and it's still TL;DR and baseless speculation is fun and all but I just think these are relevant factors that really do contribute to which civs end up in game and are worth considering.