Moodle ships with a significant number of themes. I suggest that we reduce the set of core themes to Standard, Clean and maybe MyMobile (although maybe just Standard and Clean). The rest of the themes could be shifted into the plugins system (https://moodle.org/plugins/browse.php?list=category&id=3)
We should add a "get more themes" type link to the themes page that allows installation of new themes from within Moodle.
1) Encourage users to discover the plugin system.
2) Give contributed themes more visibility.
3) Reduce the testing burden for HQ. Right now "test in all themes" is very time consuming.