A good resource to learn more about scaling flat self-organizing organizations is the book Reinventing Organizations. It's a curious mix of dreamy hippie philosophy interspersed with very practical examples of flat orgs and how they remain flat while still getting things done.
+1, I love RO. The Holacracy book is also a great read for an implementation of what a built-out Teal (though not quite flat) system can look like (and how it responds to objections like the ones seen in a lot of these comments). Of course, you have to unlearn all the stuff you learned about Holacracy from bad business mag articles....
