Yea, I don't think this would be difficult - since MusicBee is aggregating child playlists' content into folders already - so the iTunes xml would have only needed that same info... but since Steven is not interested in this area, this sounded unlikely to ever be addressed... so hope is all we can do.
On the upside, the itunes XML does order 'as if' the folders were there...
MB playlists structure:
Will arrive in the xml in the same order at least... i.e.
So there is not need to prefix/rename your playlists to force some sorting, MB already keeps the folder based internal playlist sorting order... it's just without the folders. But if you know your playlists folder/structure, you can fairly quickly navigate a very long list (i.e. I have around 300 playlists.... so that's a long flat list... but at least I have access to proper smart-crates and multi-value/custom metadata this way... opposed to the shit-show that all 3 main DJ softwares have managed to come up with in terms of library and/or metadata management... and it works surprisingly well with DVS if you have a mini-ctonroller to scroll quickly, or use a single controller for all DJing for which browsing through hardware is fairly quick to navigate a long list with as well... just mouse/trackpad interaction becomes a bit of a nightmare when dealing with long flat lists...
Hope this helps.