Id like the ability to create a user based customizable field. So in addition to late, missing, etc the teacher could create absent, in your example, or any other status they might find useful for their class.
(My request would be a "nice to have" not a must have )
This doesn't look like an option that is currently planned in the scope for New Gradebook, and I couldn't find an existing feature idea in the community, either. Would the Excused option not work for this purpose?
If you feel it's needed, I'd recommend submitting a feature idea so our product team can see if others in the community would like that idea as well, along with cases as to how it would be used.