Essentially the GMD will be made obsolete by RDA.
I am thinking that is a good thing. With all the new formats out there now, there seems to be little consistency between libraries when it comes to GMDs. For instance my library uses $h[videorecording (DVD)] for DVDs. When searching for copy I have also seen just $h[videorecording] ; $h[DVD videorecording] ; $h[DVD] and $h[videodisc]. And for downloadable materials there is any number of GMDs being used. Some examples: &h[online audiobook] ; $h[e-book] ; $h[downloadable audio], etc. etc.
With RDA there will be NO GMDs. Rather we will use a marc tag 338 – Carrier type (R) See: http://www.loc.gov/marc/changes-rda-338.html
Term for the category of carrier used to convey the content of the resource.
338 $aCarrier type term.
I am hoping that the ‘powers that be’ will provide a list of the carrier type terms to use for any given format. If not we will be back to our old inconsistent methods…