Never. There are 12-13 civs left to announce (of which 2-3 are DLCs) and 9 full weeks left to the release.
I think they will release one FLciv video per week until the week of 17-23 october.
On that last week (game is released on 21, friday) we will see first look videos of the last regularciv and those 2-3 DLC civs.
It may seem like very late reveals, in the last days before release, but for example last two BNW civs were revealed merely one week before the release so I wouldn't find that too late. It'd also make sense for me to reveal optional DLC$$$ civs last and right before the release, to hype them and boost sales (or more cynically: to not make people cancel preorder pack due to dlc content disappointment

)
I also think we'll get 21 civs on release, not 22: 18 regular, preorder aztecs and two DLC civs. Why 21, not 22? Because two of 22 rulers shown in the leak were very definitely Spanish, and I think devs at time of leak were simply not sure which of those two use for Spain (I don't believe in "dual leaderscreen" or "multiple leaders" theories).
My additional bet is: DLC civs will be Poland and Sumer (due to them being very popular demands yet non essential civs).
We'll see who is right soon...