Hahaha, quick, are there any cactuses in the picture?!
That alone is something I find interesting - that our theories and knowledge (or lack thereof) are constantly evolving. We could even be wrong about stuff that's in Civ 6 right now, and just not know it yet.
Passing psychotropics through aqueducts would have made for one hell of a civ, though, that's for sure.
Shuckee gee, the whole premise of Civilization games has been revised since they started making them: The idea that Cities started around 4000 BCE in Mesopotamia. City foundations have been found as far outside that area as South America, Anatolia, China, and southern Europe, dating back up to 2500 years earlier than that date. The whole Start of the Game should have been revised years ago.
In addition, I've got my own list for Weird Stuff that I want in a Civ game but have never seen - the difference is that these all have historical/archeological evidence for them that is controversial in some cases, but hasn't been outright 'debunked':
1. Technologies available at the nominal Start of Game (4000 BCE) include Pottery, Animal Husbandry/Domestication for sheep, goats, cattle, horses, and water buffalo, Crossing coastal waters for people and their animals, Wine Making, primitive Metallurgy (annealing and/or smelting copper, silver, gold, lead), Archery.
2. First Military Research Laboratory - 400 BCE, where they invented the crossbow, catapult, and Quinquereme warship
3. Firing Artillery as an Olympic Event (almost, it was actually one of the other Greek games in the same cycle as the Olympics)
4. Chinese discover the Americas 50 years before Columbus - having better ocean-going ships than he did.
5. African civilization goes straight from Neolithic to Iron Age without ever using Bronze - and starts using fairly good steel several centuries before anybody else except:
6. India has high-grade steel around 400 BCE, long before anywhere else in the world, because of a peculiar combination of monsoon-driven high temperature blast furnaces and high-grade iron ore in the same place.
7. The only ships that were ever Upgraded using the same hulls and weapons were Ships-of-the-Line and Frigates - major navies like the British and French added steam engines and propellors to most of their SoLs before scrapping them for Ironclads a couple of decades later, and many Frigates were converted into Steam Frigates with the same rigged masts, guns, and hulls.
8. British, French, Japanese, Americans all converted Battleship-type vessels into Aircraft Carriers, but it required much more extensive rebuilding of everything above the waterline. Used the same hulls and machinery, though, and produced, until 1945, the largest Aircraft Carriers in the world (in Japan and the USA).
- And that's just a sampling. There are so many intriguing things historically that have been ignored even in the Uniques and 'special' attributes of Civs in Civ games that even a handful of them would make a very different kind of DLC . . .