We would like to have access to users for custom fields to assign the review of a task to a person without changing its owner
@Eddy_Boels, subtasks will work for that case. Custom fields are for storing meta information about tasks/items, not for task-management.
I would like this feature to use for persons who are consulted but not responsible for the task. It would be very useful to keep them informed without assigning them and thus keeping the task clean