@todo comments mean that there is something in code that has not been finished yet.

You will also find a note in administrators guide that the option is not yet implemented.

I don't see any place in code where the settings are used for something that can be seen by a user.

Do you agree that I can close this issue?

Hello atrol
Those variables are used in "user_pref_api.php"

class UserPreferences {
-> private static $_default_mapping
... 'email_on_status' => array( 'default_email_on_status', 'int' ),

which is later user in a config_get().

They set the status for options in user preferencies:
E-mail on Status Change
E-mail on Priority Change

You are right,
I noticed the variables in UserPreferences, but didn't notice that they are used by configget without the starting default

Seems we should change the source code comment and the administrators guide.

Fis is part of PR https://github.com/mantisbt/mantisbt/pull/1454