If nothing else Dunbar's number will creep in somewhere. And of course the whole reason we don't use flat hierarchies unless the company is really small is beca

If nothing else Dunbar's number will creep in somewhere. And of course the whole reason we don't use flat hierarchies unless the company is really small is because of the explosive growth in the company communications graph. People could form ad hoc teams to reduce the exponential growth (instead of having such teams pushed on them by management), but then it's not a flat hierarchy anymore. Instead it's a self-organizing construct which may or may not be better than actually designing a proper org. structure.