To be honest, I’m a little bit astonished that nobody ever mentions that nested circles are just another form of representing a hierarchy. Every serious relational database developer — as well as most programmers—should have heard of Joe Celkos Nested Set model which is one approach to manage tree-like structures in a relational database.
Additionally, from a structural point of view, there’s really no difference at all in calling a group of people a circle, a department, a team or a bunch, clan or squad, chapter, guild…just another label for the same thing.
Therefore, to me Holacracy is not about a different organizational structure. It just tries to add some dynamics and additional interactions (which is valuable of course, but not revolutionary at all). Both can be done in a traditional organizational structure too: basically by re-aligning decision making with value creation.