The `bootstrapbase` theme was added in Moodle 2.5 (June 2013 = 2.5 years from the 3.0 release), and was made default in Moodle 2.7 (June 2014 = 1.5 years from the 3.0 release).

Since then, the `base` theme has been less and less loved, and is gradually becoming technically expensive to maintain: It requires additional development time, especially for new JavaScript-based features; it requires additional testing time each week, and with various issues surfacing to clean up bits of the theme's CSS (MDL-50990 for example), it also requires dedicated integration time.

In addition, the base theme uses old practices, which in turn rely upon deprecated libraries which we wish to remove (cssreset from YUI).

I'd like to deprecate the `base` theme as of Moodle 3.0 and remove it as per the standard deprecation policy in Moodle 3.2.

Steps required to deprecate the base theme:

1. raise a discussion regarding this change on moodle.org's theme's forum;
2. add some warning that the `base` theme is deprecated when it is used as a theme parent;
3. update the theme upgrade.txt.

When it is removed in Moodle 3.2, it can be moved to the plugins repository as usual.

As the `canvas` theme also depends upon base, this will also need to be deprecated and removed in the same manner.

Note: None of the themes marked as supporting Moodle 2.9 in the Moodle plugins directory use either base, or canvas.