I wish you would reconsider the decision or at least adjust as I suggest below.
Having private Q&A is much different in my mind than public Q&A.
The logic/argument that making it all public helps everyone misses the point of private Q&A entirely. Those that choose to use private Q&A do so precisely because they do not want their questions public. Why is that? For me, there is almost always specific mention of URLs in my questions. Not only do we not want to raise red flags and reveal issues for potential COMPETITORS to find, we often do not want CLIENTS to be aware of the conversation as we work to resolve issues or make changes to improve performance.
The other reason I like the Private Q&A is that the quality of private answers is simply higher and more reliable in our experience. Having a fallback resource has been a great comfort when we step out of our areas of expertise. Losing that is a negative, no doubt.
ONE WAY TO LESSEN THE EXPOSURE OF A QUESTION THAT NOW MUST BE PUBLIC (but that we do not wish to be public) would be to add in an optional check box that disallows indexation by the search engines. That way, it at least makes it harder for those outside seomoz.org to discover the conversation.