I don't think this is a Beta/VHS issue. That was about licensing and Sony wanting to keep hold off all the technology - as Apple has done.
M-D was accepted and generally thought that it would become the new cassette. Then came MP3.
Whilst I agree with the sound observations
of other PPRuNers (I am a M-D fan myself) I think that MP3 will win.
It will do so because it is seen as 'new' and easier to sell. It is seen as flexible because the memory can be reused. I think that one of the fundamental differences is that those of us here probably represent the 'older generation'. [Ducks to avoid incoming] We tend to collect music.
The kiddies of today tend to move through music, copying, listening and discarding. For this, once you have pursuaded Dad to buy a PC with a CD burner on it (and they are VERY cheap now), then you can download and burn CDs in MP3.
A portable CD player is waaaaaay cheaper than a portable Mini-Disk.
So, age and money!