I totally didn't even realize this, N'Zoth is the final boss and BfA was totally supposed to be the Old God expansion that people have been asking for. I totally thought BfA was leading up to an Old God expansion with maybe like the rise of the Black Empire or something. But nope, I'm pretty sure Blizzard intended for BfA to be the Old God expansion and I don't think people had any idea.
Yikes.