So it seems there is a median projection of mild decline way in the future. There are also reasonably probable scenarios that show no decline, or more precipitous decline. However, they generally agree that there will be at least 1 billion more people in the world, most likely 2 billion, and possibly more.
What is the real risk of the Earth eventually going back toward having 8 billion people after reaching 10 billion? Why is this "the exponential process one should be most concerned about today"?
The real risk is the TFR never rises and population drops until complex society cannot be maintained. Or perhaps some weird minority with higher TFR takes over the world, what I call the "Amish Scenario".
Are you talking mainly about demographics? Like not enough working age people and too many older people?
Yes, and also that if the population becomes small enough it becomes impossible to sustain an industrial society due to lack of scale.
Isn't most of industrial society really just trying to deal with the problems of having to sustain so many people?