Thinking about this some more, a simple "comments" field that's not visible to students would both a) be useful for many of the same uses and b) be readily extendable to what http://martinfowler.com/bliki/UserDefinedField.html mentions as the first option.
We don't really NEED to add three fields, we could use a comments field and for our use case we'd fill it out like this:
Position: President
IQ: 82
Predecessors IQ: 83
The Fowler link mentions storing custom fields as LOBs, such as XML or JSON inside the "custom data" field. One could implement a text field pretty simply which users could use however they wish, and later recognize if the text in that field starts with <moodlecustomdata>< ....
Any thoughts on having a comments field that teachers, managers, etc. can use for whatever need they have?