I am equipped with very limited clairevoyant abilities.
So I am not able to say which turns the future development of players will take and which of the standard (as in "can be used by everyone") fields will be used.
What I can say: it is rather short-sighted to use the Windows Explorer with all its limitations as tagging program. MP3tag is the program of choice for this purpose.
See the help for a list of supported fields:
Or you write a little tagging program of your own and use the PRIV field which can only be handled by the originating application. It is a standard field but is usually ignored. And as standard field it won't get deleted by WE.