It would be very useful to have groups available. So the groups could be assigned to a project instead of assign explicit every user to a project: time-saving and easier to manage many user accounts.

The group could be implemented as an additional user field. Maybe as an self defined custom user field and be queried by the Mantis-Core-API user_get_field( $p_user_id, $p_field_name).

Using Mantis authorization within DokuWiki this feature would allow a better page access by group policies. For instance developers could be separated in groups according to their office locations and only be allowed to edit their own office pages.