Speculating on the new civs:
I drew up
this spreadsheet a while back quantifying the most notable civs absent from Civ 5, based on past appearances. The most notable absences are Mongolia, Babylon, and Zulu, but I'm not 100% sure we'll see all three in R&F. Babylon is a little too close to Sumeria, and there's always a chance they'll opt for a new civ over Zulu, who've been the most frequently featured African civ across the series. Beyond that?
Likely:
Mongolia
Korea
Dutch
Inca (or another Native)
Ottoman Turkey
African civ, possibly Zulu or Mali
Possible:
Carthage
Celts
Babylon
Italy (I don't really buy the Italy tease in the trailer)
Byzantine
Other Latin American (Argentina? Mexico? Colombia?)
Other Native American (Iroquois? Comanche?)
Another African civ. Wouldn't be surprised if they try to represent both west & south Africa
If I had to guess, I'd say we see 5/6 of my Likely picks –– let's say Mongolia, Korea, Dutch, Inca, and a new West African civ, maybe Nigeria or Yoruba. There's a solid chance Turkey gets added, possibly at the expense of one of the above options. Not only are they a very notable absence, but they fit the "well-suited for a bonus related to new expansion systems" line from the announcement.
For the other three civs, I would wager on a modern Latin American civ, such as Argentina or Colombia. A North American native civ or a second African civ to cover South Africa – could see the Zulu return. Finally, I could see one more Mediterranean civ being added, whether that's Italy, Carthage, or the Byzantines. But to be honest I would expect Ottomans to make it in before any of those three.
So my speculative lineup could include Mongolia, Korea, the Dutch, Inca, Nigeria, Turkey, Colombia, and Zulu.