Definitely need this as I have not yet found a way to do this with any other fields except for the email field. There are no other AD records coming across that I can use to distinguish this. Unless you can bring the AD/OU/group across that is being read. If I had that then this would also be an easy field to filter staff from customers/students.
We recently added the ability to create "manual" requester groups, where users can be added explicitly instead of configuring rules for them: https://support.freshservice.com/support/solutions/articles/50000001678-create-manage-requester-groups
We currently haven't roadmapped the ability to add users to requester groups based on their email address. We'll pick this up at the next available opportunity.