Just a thought....
Correct me if I'm wrong but one of the reasons that MD and HiMD have been hobbled as a truly flexible format for free transfer of music is to do with internal restrictions imposed by Sony to satisfy its music publishing arm.
Perhaps Blue ray DVD could offer the corp a way out? As it is a new technology it may not have the same restrictions built in (though I should imagine they probably already thought this one through).
A 48GB interchangeable and rewritable media format would blow fixed hard drive players out of the water - get the transfer speeds to a decent rate (and allow unrestricted, two-way transfer BTW) and perhaps develop dedicated portable music, video or data recorder players (or combinations of these).
The only thing is that MD would be effectively become a redundant