I noticed that since version 2.25 of the RSS extension, the reverse attribute seems no longer to work, e.g. the displayed RSS feeds are by default always sorted chronically ascending (oldest to newest).
Still occurs in the current 1.35 master of the extension.
One can fix that by editing/changing RSS\includes\RSSParser.php line 71 $this->reversed = true; (default)
to
$this->reversed = false;
though, (which I did on my mediawiki)
I call the attribute in the article template with <rss template="News-feed" max=3 reverse> as described here.
Maybe I'm doing something wrong there since all the other attributes use an <attribute="" > notation style?