It is my feeling that while Atheism-focused sites have been wildly successful on the internet as a whole, a trend is that those seem to be discussion-oriented as opposed to being well-suited to a question-and-answer format.
I don't think bringing in more well-known people who can answer questions will fix this fundamental concern: there just seems to be a finite pool for the sorts of questions people might ask, and many of the sorts of questions people might ask are going to be more heavily debatable-opinion-oriented than citation oriented. This makes me think that the trouble is in the definition stage rather than in the commitment stage, where bringing in more subject-matter exports or higher enthusiasm might be viable.
For example, looking at the old proposal, of the questions rated > 10:
2 are duplicates (1 and 4), but you can see in the comments how it immediately changes into a back-and-forth discussion on both of them. (3) is a pure opinion question that is on the Atheist FAQ. (5) is exceedingly general, but also the sort of thing that comes from a relatively limited answers pool. (6) is really a variation on (5). (7) is a pure-opinion/discussion question (evinced by the use of the word "you").
Of the questions, at least half of those top ten feel like the sorts of questions that get asked of atheists, not the sorts of questions atheists would seem to ask one another, or even really the types of questions someone asks who is looking to become an atheist. So you may get the odd "drive by question" from an outsider, but that doesn't really support a community of back-and-forth questions and answers.
We see this starting in the proposal for the new site as well, since "What type of evidence would be sufficient for you to start believing in one or more deities?" is a question that each individual could answer personally for yourself: It is an open ended question that relies on the opinion of the poster.
Meanwhile, I think Skeptics.SE has great potential for a stack exchange site, and has been in beta for 308 days as of this writing. There are of course challenges with definition, etc but the core concept could have a great deal of traction for a Q&A format.