If this is true, it means that they reveal 17+1 civ until NDA falls.
I'd say that there is a chance that it actually means that there will be 18 games in the base game,
including Aztecs. If that is the case, I can imagine that half of these forums goes into rage (myself excluded).
If there were 2 unrevealed civs on Sept 29th, I would think it is just the way they do it and it is going to be 18+1. But if it's only one, I'd say it's actually none.
Just posting this so you can take it as a possibility and get prepared
Like I said, I won't be mad, but some people will.