Support rich text in Media Viewer's download and embed features, along with plain text and raw HTML.
A rich text option would invite me to copy and paste a simple phrase with embedded links such as this one:
Instead of only offering me this raw HTML:
"<a href="https://commons.wikimedia.org/wiki/File:17_Years_of_Sekar_Jepun_2014-11-01_42.jpg#mediaviewer/File:17_Years_of_Sekar_Jepun_2014-11-01_42.jpg">17 Years of Sekar Jepun 2014-11-01 42</a>" by <a href="//commons.wikimedia.org/wiki/User:Crisco_1492" title="User:Crisco 1492">Crisco 1492</a> - <span class="int-own-work">Own work</span>. Licensed under <a href="http://creativecommons.org/licenses/by-sa/4.0" title="Creative Commons Attribution-Share Alike 4.0">CC BY-SA 4.0</a> via <a href="//commons.wikimedia.org/wiki/">Wikimedia Commons</a>.
At this point, many programs can accept the rich text option via copy/paste (most CMSs, like Wordpress, have rich text editors; *Office; all modern email clients; etc.).
Thanks to Luis Villa for this suggestion :)