Not all the extensions in /branches/wmf/1.16wmf4/extensions are actually enabled on any WMF wikis. Extension:Configure, for instance, is conditionally included in CommonSettings.php but disabled for all wikis in InitialiseSettings.php. I wouldn't count that as OnWikimedia, although maybe I'm just being pedantic.
Topic on User talk:P858snake/Archive 1
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Well the extensions have gone though the review process and been approved to be branched into it for a reason so they most likely being used somewhere (such as the test sites).
'wmgUseConfigure' => array( 'default' => false, // 'testwiki' => true, // disabled bv 2009-03-25, will return to it later ),
It was being used on the test wiki for some period of time a while ago, but it isn't now, as far as I can tell.