Monospace textareas applies like it should in many textareas, including this one (https://secure.phabricator.com/maniphest/task/create), but it doesn't seem to be enabled for inline comments on diffs.

1. Enable 'Monospace Textareas' on https://secure.phabricator.com/settings/panel/display/, then Save.
2. Go to a diff, say https://secure.phabricator.com/D1337
3. Make an inline comment, type some text. "1lI|".
4. The text isn't monospaced.