Custom attributes should optionally support having both a name and a value at the point of definition by the system admin.
They would be as currently assigned to users/teams/group as
appropriate. The value of the attribute could then be set at this time or by the user, team/group owner in a custom attribute extension to the user profile or similarly for for teams and group. Support for attributes of type simple
(no value, current behavior), required (must be set), overridable (can be changed or not from value set by system) could also be added.
An extension to markdown to return the value (could also contain markdown) of an custom attribute would also be useful e.g. "I have the following hobbies : %Hobbies%"