How do I add a currently unsupported field to Views?
You will need to add the field manually to:

drupal/modules/views/components/civicrm.core.inc

and then submit a PR to civicrm-drupal repository, so the fix gets merged into the main code base.

In D8, the situation is a lot better, as torrance has automated the process and the fields and their definition get picked up automatically. So a lot cleaner and easier on everyone.

But for now, the above is your best bet and will help views intergration for D7 and prior