It looks like the teasing was leading up to exactly what many suggested it would be leading up to. Firaxis has announced Gathering Storm, a brand new expansion pack for Civilization 6, and the second one, following Rise and Fall.
Gathering Storm will be the single largest expansion pack Civilization has ever gotten, and will be adding quite a lot of things to the game. Features from Brave New World, which were missing from Civilization 6, such as the World Congress, and diplomatic victories, are being added back to the game, while the game is doubling down on dynamic environmentalism too.
Natural disasters like earthquakes and volcanic eruptions are also a thing to contend with, usage of resources like fossil fuels will have effects for you to consider, and you can directly change the lay of the land with engineering projects. All of this, plus new civilizations, new leaders, new buildings, new wonders, a new future age, and new scenarios are being added to the game too.
It sounds like a very full featured expansion, and hopefully the final game benefits as immensely from it as Civilization 5 did from Brave New World. Civilization 6 is out now on PC, Nintendo Switch, and iOS. The Gathering Storm will launch for the PC version of the game on February 14, 2019.