MDL-62708 added idnumbers to the Moodle question bank. (We hope. Assuming that the integrators don't reject it.) At the moment, we took the decision that we should not display then in the UI, because usage will be limited at first. But, in due course, we will need a way to display them.

To do that would require:

1. Make a new 'column' class in question/classes/bank (it would need to be similar to https://github.com/moodle/moodle/blob/master/question/classes/bank/question_name_column.php).
2. Decide whether to add that to the default used if $CFG->questionbankcolumns is not set: https://github.com/moodle/moodle/blob/master/question/classes/bank/view.php#L125 (probably not at first).
3. Document $CFG->questionbankcolumns in config-dist.php