When on the Users page, I can filter my user list using various custom and/or default fields. This is very convenient for group actions, like messaging a number of users together.  I would like the same capability to exist for enrolling users into courses/classes and paths.

Filtering functionality on People Picker is severely limited, allowing you to only select from Groups, Courses/Classes, and Organizations. 

If you need to enroll a set of filtered users into a course/class today, I believe the only option is to export a list of users, filter it via Excel/Sheets, add course LMS ID, adjust the format, save as csv, and use the Import > Enrollment feature to enroll those users.

Adding User filter functionality to the People Picker, or adding enrollment capability from the User list (like you can do from a user's profile page) would be very helpful.