1) Ability to preview private messages.
2) Option to save a copy of a sent private message.
3) A relatively easy way of getting rid of the threaded/nested display modes, so that only the flat display mode is available. Having to edit a few files is ok, as long as the procedure is documented.
4) Integrate public and private forums by using a common access method. I.e., each forum's access is determined by who can access them and what rights they have.
5) Addition of a switchable "view" privilege for forums. A user with only the "view" privilege can see the name/description of the forum on the main forum page, but cannot "get into" the forum. A user without the "view" privilege for a forum will not see the forum at all.
6) Add a reply-only privilege for forums.