Hi! It seems like You have got an idea similar to what I'm thinking these days. A Wikipedia with fictional content. You may be focusing on fictional universes as in books and other media or existing in individual minds, while I'd rather think of a place where any fictional information can be explained systematic and organised. As an example i'd like to promote the idea of micro minorities as the concept of individuals having their unique personal properties. The only place it existence is http://www.mikroitet.dk, because the moderators at Wikipedia didn't like me writing about thing I invented myself. So, if I'd want to have a place for anything fictional and semi-fictional, it might not fit with your idea of a ficipedia?
I've discovered that there is something at scratchpad.wikia.com : http://scratchpad.wikia.com/wiki/Fictiopedia http://scratchpad.wikia.com/wiki/Ground_rules
But this is a very specific angle at fictional content. My question to You is then: would You be interested in making af wholly top level domain wiki with fictional content of any sort. By idea is basically to use sets of categories to define in witch degree the content is fictional. Anyone can write what they find interesting to describe for the world to read, as long as it is more than plagiarism as http://www.uncyclopedia.org. Well, it has just arrived at Fictionpedia.org http://www.fictionpedia.org !
Go tell Your neighbours and go write some fiction!