The ability to hide certain users from the ticket assignment dropdown / to disallow certain users from being assigned to tickets would be a particularly useful feature for us.

A potential use case is if a shop has some non-tech staff (reception / admin) that don't work on tickets, they could also be removed from ticket assignment. There is an existing suggestion to require tech assignment upon ticket creation that would solve the problem of default ticket assignment if the ticket is created by a user without the permission to be assigned as the tech for a ticket.

In our case, we have a few users with very limited privileges we use for testing anything that uses the API on the live RS instance for the first time, and whilst people know not to assign those users to a ticket it would be nice to enforce that with a group permission to avoid it happening accidentally, and to avoid 'cluttering' the assign-tech dropdown (all names and emails have the prefix API-, meaning they show up first in the list of techs)