I do add metadata to my LaTeX documents since more than a decade.
hyperxmp provide an interface to do so. Recently the possibilities have expanded with hyperxmp. You can add more and more stuff. In theory, this looks great.
I started asking myself who actually uses this metadata. Tags like
pdfcontactphone are hidden well behind nested windows in Acrobat. I did a quick test in Acrobat DC by specifying
pdflang and reading the document loud. To my surprise Acrobat does not care. Even when the text-to-speech packages are installed in Windows and the language is correctly specified in the PDFs the reader does not switch the voice.
So, can you give examples where (XMP) metadata make a difference today in real life?
Where is the advantage of having the authors in a list instead of a single string?
Who cares about multilingual document titles?
Realized use cases of author contact fields?