Well I've just noted this when updating my example websites (see issue 16): The HKP draft defines that option=mr which gives back machine readable responses.
I case of op=get it (absolutely reasonably) returns the key "as file" (and not as HTML page) with the correct MIME type.
In case of op=hget that doesn't seem to work, although it would be a reasonable candidate for the same behaviour.
But,... I personally have absolutely no real need for this, as I never use hget.
In case this should be implemented, please notify me, so that I can send you adapted versions of my XHTML+ES example site, which then allows the combination hget + mr.