Here he explains about the expansion:
https://civilization.com/news/entries#announcing-civilization-vi-rise-and-fall
The full announcement trailer can be seen here:
And here the Steam News announcement:
http://steamcommunity.com/gid/103582791454551861/announcements/detail/1465222576769486958
New features from the blog post:
- New civilizations and leaders (8 and 9 respectively)
- Golden and Dark Ages, based on loyalty
- A new Loyalty system, impacting cities and more
- Governors to place in your cities
- Enhanced Alliances
- Emergency situations to deal with
- Historic moments
And more to come!