What I'm most worried about is that Wikipedia will lose contributors, because most of them won't get a choice to decide what's in the "real" encyclopedia and therefore lose interest. The closer (the more "officially") Nupedia is associated with Wikipedia, the less interesting it will be to spend time for Wikipedia, because everything one is doing there is just the "foreplay" for the "real thing" Nupedia.
This might be fixed if there's some more automated way of adding articles to the 'stable' version of the encyclopedia. All potential solutions require more software, but there's a number of them (which is better I'm not sure yet). One of the many would be to have a process similar to the way Debian's distribution works (with regards to 'testing' vs. 'unstable') -- all revisions articles automatically get promoted to the stable version after some period of time (a week? two weeks?), unless someone marks it as "not ready for stable". Then presumably there could be some process by which either that mark can be removed, or it can be overridden by a consensus of everyone else.
But really I think something more automated like this is necessary, because I don't think the Brilliant Prose page is every going to have 15,000 articles on it, and even if it does, will be impossible to keep up to date.
-Mark