Hey Chris,
While adding custom fields to an export CSV of Attendees is still something that would require custom coding, at this time, there are some filters and actions you can use to pretty thoroughly customize the actual columns on the Attendees page, and that can be quite useful.
An example of one such customization is one I did recently, in fact, where we helped a customer tweak the columns so that they listed the attendees’ phone number. Check that out here if you’re curious → https://theeventscalendar.com/support/forums/topic/add-attendee-telephone-number-to-attendee-list/
Another note is that the Attendees list uses the WP_List_Table class, something built right into WordPress itself, so if you research things about tweaking that class, you will by extension learn a ton of ways to tweak the Attendees list within our plugins’ admin screens.
I hope some of this info is helpful here – let us know what you think!
George