Enable scales to be mapped to numerical grades

We have a number of professors who would like to evaluate some of their students' assignments with a non-numeric grade using a custom scale, but would like to have the Moodle gradebook appropriately calculate the values. Obviously Moodle cannot know what numeric value to assign when the grade assigned is non-numeric, so I'd like to request an improvement/feature to allow custom non-numeric scales to be created while also offering the option to provide numeric equivalents for each of the non-numeric items.

I understand this process can be achieved by providing a non-numeric equivalent for numeric grades, but some professors would rather enter a B+ for example instead of having to remember that a B+ is actually the potential numeric equivalent of 4.33. This feature of assigning numeric values to non-numeric grades is available in Blackboard.

Thanks so much for your consideration.