An expert-only fork will lose something very valuable, I fear. For example, I know very little about the English Civil War, or the Battle of Trafalgar (I had "trendy" history teachers at school who steadfastly refused to teach us dates...) Yet today I've been looking around these pages and those that link, fixing links, correcting typos, and occasionally rewriting for clarity. The risk of having only experts write a set of articles is that only the experts will want to (or be able) to read them. Outsiders to a subject give the layperson's perspective.
I'm all for a "safe haven" for good articles, something that will attract experts to Wikipedia. We DO need more people who are knowledgeable, in many subject areas, but not at the expense of shutting out the hoi polloi.
I suggest that such a safe haven be non-editable: a presentation of the best of Wikipedia, not a forking. It can attract experts, who will marvel at the quality -- but to make a contribution, they have to go into the fray of the main Wikipedia.
-- tarquin