The readership stats could be interesting.
See here for what is known for Wikipedia.
To generate it, as far as I can imagine, some logs of our servers are necessary. If I knew the format of the log file, I hope I could write an analyzing script in python. Well, I guess the logs are confident, at least as far as the privacy issues are concerned. So the script could be run by CZ technical stuff once a week(month?), say, on a server. As long as we have a few thousand pages in the mainspace, we can do the full editcount (probably later we should restrict ourselves to most popular pages only).
Another interesting report could be constructed from what is inserted in the "searchbox" ("what do readers want?"). I imagine that there is a log file that keeps track of it.
BTW, concerning wikistats (citistats?), as number of authors, active authors, new authors, new pages, edits in the database etc., something has just been published, see the Citizendium-L
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