At one time I thought I had read that there was a group of MW users who were getting together to discuss more 'business' needs in wiki.
Well, I remember having been involved in this: http://wikis.wikia.com/wiki/Wiki_sales_pitch But that's not exactly what you're looking for. There's also Enterprise Wikimania, hosted by Socialtext: http://www.eu.socialtext.net/ewikimania/index.cgi Though that's pretty much dead as far as I can tell (and it's obviously not focused on the MediaWiki engine either)...
Is there a better place to put up questions discussing possible extensions that would probably never be used in WP worlds but would be better aimed at usage by business. Is there interest in such?
I would certainly be interested in that, but I'm not sure whether or how I could contribute...
What kind of topics - other than the obvious access restrictions - are you thinking of?
-- F.