Doesn't happen. People naturally seek out authorities and instinctively elevate and listen to them. Even if no one bears the formal title, there will be a few people who end up directing the group.

Far from eliminating political barriers, "unstructured" groups make them supreme. Without granting explicit designations for authorities, the only thing holding the group together is popularity. This means the best propagandists and most personally charming leaders (read: best flatterers; the people most willing to tell you whatever you want to hear) will be in control, regardless of their incentives, motives, or true qualifications.

They've written it down in more detail than "shared responsibilities" too. It's a pool of self-employed freelancers handling projects in their own way paying fees/commission to a holding company with dedicated admin/sales responsibilities and major decisions made by a board or by vote. Paid projects people don't want to handle themselves go to the first person to indicate interest unless the interested parties agree otherwise. It sounds more like a non-profit, elected-board, closed-shop Uber than "shared responsibility".

Needless to say, this model is not going to work quite so well with every type of creative process and personnel.

ActUp used to give managerial lessons for leftist organizations. Of the materials I saw, one of the things they used to teach was that a truly flat organization results in informal hierarchies developing, by the people most capable and/or passionate (because they're motivated by the issue primarily). But then these people are most likely to burn out, because without formal recognition of the power they need to achieve that role or the formal hierarchy in place around them, they end up taking too much on themselves to cover the holes.

But they were talking to leftist organizations. Often these people had communist / socialist / anarchist ideologies, so you can't just tell them: "Implement a hierarchy". And even when they weren't leftist, they were often all volunteer organizations, so you had the same problem anyway.

So their solution, was that when you set up a new organization, you start with it flat. You identify who takes on what roles, and define those roles formally. As you define those roles formally, you define what people have to do to get into that position, clearly and openly.

And that's it. You're still flat, because the positions appear to be emergent. You have a hierarchy, but no one feels like they're stuck under the rule of a shit boss, because everyone in those positions are meritocratically elected, there's now a culture of free movement between positions and definition of positions, and what you have to do to move from one position to another is transparent, instead of opaque as a way for people above to keep their position of authority.