Custom fields are hard to manage and visualize in the current flyout window format.
If there was one dedicated page that would allow me to see what custom fields are being used, in which space, folder, list and more. I'd want to be able to see on this page the name of the custom field, the type, the description, the location being used, etc.
This would help me and my team to see clearly what the library of custom fields are, what their purpose would be, avoid duplicate custom fields (ie. having a website custom field 9 times even though each URL custom field serves the same purpose).