The Apache Foundation provides an excellent place to start and a wonderful model for Sakai to emulate. It's proven its durability, agility and scalability. http://www.apache.org/foundation/how-it-works.html
I would recommend flavoring the Apache governance model - tightening it, perhaps - in recognition of the mission Sakai serves. Apache is agnostic and can afford its completely open style and a promiscuous, if not profligate, multiplication of tools, contributions, and extensions. Sakai's mission is more specific: unleash learning and teaching in the virtual world for higher education institutions. There are more fixed knowns, and more at stake in that specificity. In my world of 64 *** campuses, there are also responsibilities to timelines, the rhythm of the academic calendar, training. Further, there's urgency to develop working, robust solutions responsible to core academic values and not commercial ones.
My gut tells me, then, and I humbly suggest, that there needs to be an executive layer between Board and Project Management. It should be finite in its responsibilities, and those should center on specifying deliverables and keeping the core values of the higher ed mission burning bright and true, plotting strategy and business matters with the Board and being responsible for executing it. This executive branch should be linked (again, I'm going on gut here) to a layered approach to the universe of Sakai deliverables itself: there is a Core Sakai technology, set of tools, etc, kept by that executive entity, and then everything else in a Darwinian environment whose value derives from use and elegance.
For this Executive entity, I imagine a very small number of people, preferably one, maybe three or four, not two. One firm person who is responsible for a clear vision can control chaos better than a committee. And Sakai's greatest liability has always been that chaos looms.
I know it's not pc, and may go against the grain of the open philosophy driving Sakai to success, not to mention academic etiquette (which is largely anti-executive, God bless us) but I heartily recommend you at least consider its value.