The extension is enabled (wmgUseRSSExtension, wmgRSSUrlWhitelist) for the following wikis and feeds in wikimedia farm:
(code
<rss max="6">feed url</rss>
is used for examples)
Well the case of the last URL is clear — bugzilla got moved to phab. As to the rest I can open them all in my browser and they indeed are feeds. Some now have https instead of http so I blamed it at first, but though it might be worth fixing it proved to be not the case as some are already written in https form and some of them are working and some are not. The most interesting is wmfblog — it works on WMF-wiki but does not work on MW-wiki though the URL is the same.