Would you consider adding a new field to the output of MCWS' Library/Fields endpoint, that indicates if a field is a User's field?
I just wrote a tool that surveys the usage count of all of the fields in MC, and would like to be able to detect which fields properly belong to MC vs. which are User fields. Many MC fields are identifiable via their EditType being 'Not editable'. But many others are not.
Thanks for considering.