The Orpheus Chamber Orchestra is one of the few well-known conductorless orchestras. I learned about them from an article in Fast Company, at http://www.fastcompany.com/39214/leadership-ensemble . One of the problem with no leadership at all was "We needed twice as many rehearsals just to try all of the ideas." Orpheus instead decided to organize leadership around core groups, where those groups, or membership in those groups, rotates frequently.