Issues
We've had a lot of issues with moin in our larger environment. This isn't a rip on moin or its developers, moin is a fine wiki but its no longer the right wiki for what Fedora needs it to do. At least not in its current state. Another issue, and I'm just throwing it out there, is that "its coming" or "it'll be in a future release" gets mentioned a lot yet we are still having problems and its getting worse, not better, because our wiki keeps growing.
Page saves
Page slaves are slow because of the way moin does notifications. It iterates over the users in the users dir to figure out who to contact. Combine that with a ton of regex's and moin becomes unresponsive at times.
References about this problem include: http://moinmoin.wikiwikiweb.de/FeatureRequests/GlobalSubscribeRegexUserList
and
http://moinmoin.wikiwikiweb.de/MoinMoinBugs/GetSubscribersPerformanceProblem
Logging
Right now moin does not work over NFS if two instances are connecting to it. Multiple http threads talking to the same log file from one machine works, but over NFS it does not. In our case this makes it impossible to load balance properly without something like GFS. (which has way too much overhead for a damn wiki)
Page searches
Full text page searches take a long time and cause high load
Page categories
One digg to a category and the whole site comes to its knees. I believe this is because page categories work the same way as users, iterating over each page and not keeping an index.
Also, aggressive search engines have triggered issues in the past.
ACLS
Acls in moin are fairly not-so-flexible and leave us without many ways of selectively and easily restricting a page. Additionally page defaults leave an enormous amount to be desired. If this is an unfixable problem then it may, eventually, become a deal breaker.
Requirements / requests
Please work as closely with upstream as possible to implement these changes. Maintaining a fork is a sign of failure of communication or compromise but some times is needed.