Interesting point. Just read about Coase's theorem of the firm. Isn't it slightly narrower than the ceiling metaphor? a firm expands "until the costs of organizing an extra transaction within the firm become equal to the costs of carrying out the same transaction by means of an exchange on the open market." That's a price related argument. The Dunbar limit doesn't.

This is where I would push, if Dunbar's number is a manifestation of the same thing, shouldn't it move when the price moves? Coase's ceiling has moved over time, while Dunbar's limit isn't. What's happening there?

The intersection in this case comes from source of truth information getting out of date with moving code. You can't tell whether its wrong until its been acted upon. So people stop trusting the docs, which is where Dunbar's number comes up again