Low bitrate music snapshot of collection

So I have a large music collection on an external hdd and if I'm travelling I like to do some work on hot cues memory markers playlist ect. Plugging in my hhd when I'm on a crowded train can be awkward. I suggest a feature that would in effect make a very low preview version of the song and when the hdd is not attached then you could go into a (low res) mode and do all your changes and when the hdd is plugged back in again the full bitrate music files will retain that information. I haven't done the maths on the sizes that the low grade music would have but just wondering is this could ever be a viable feature