Before rockbox there was some PC utility that would read the whole Jukebox file list and then generate a series of randomised playlists numbered 01 to 99 which covered everything. As such, a roundabout way of getting a global shuffle.
In a way I think this is quite interesting, these days the idea of shuffling songs from your entire collection is very commonplace, but before large-capacity mp3 players people hadn't really thought of doing that before, so perhaps it never made it onto 'features people want' lists. Its obvious now, maybe it wasn't obvious then.
Was there any thought given to a global shuffle feature?