I've been reading some other posts on here. Tags would be great, that way you can mix in Groove Music Pass songs as well as what is on my computer. But what you would need to be able to do is select multiple to filter on.
At current, at least on my phone, you can only select one genre at a time. But what if I want to listen to Game music and classical at the same time? So maybe the folder thing is more about introducing a greater ability to filter your music on certain things. But they can't just be the normal Artist or Genre tags either, have to have the ability to add custom tags to it.
After talking to a few Twitter users as well, the other thing that came up was that what would be really handy would be a way to limit the sources of the music by toggling the sources of the music on and off. So I can open up a list of my known folder structure, un-tick the the Christmas sub folder and then when I hit shuffle music, it no longer will play Jingle Bells in the middle of August...
And I would love Groove for ever if you could add in rules to the tags or sources filters that will automatically add or remove the music from the collection. So if I take that Christmas tag or folder and set a rule that says it's only in the music collection during December!
And on a side note about filtering sources, it would be great if my phone had an option to automatically shuffle in music from the cloud sources when connected to a non-metered internet connection and then when I go back to 4g, it blocks all those songs and just gives me the local content only.