metadata tags

In the spirit of wouldn't-it-be-nice, I'll put out a request for a better idea. 
I think we are missing the boat a bit with respect to the metadata tag, but I am
not sure of the solution.   Consider GCMD, for example.   You have included DIF
as one of the metadata types, but from a client point-of-view, that is much less
than what can be done.

Consider for example, HELLERMAN,  which is a GCMDID.   With that id, I can ask
the GCMD for many versions of the metadata, including I suppose the DIF document
itsself (though offhand I do not know how to construct the URL to get the DIF).

Sample url (html):

Obviously if I am writing an HTML client, the html version would be nice.  If I
am editing DIFs, I probably want the DIF version, etc.

So are these different metadata?  Or are they metadata-services on the same
metadata, i.e. I can get it translated by various servers?