Collaborative playlists are great, but can be better. Should be easy to.
Because there is no restrictions to whom can edit your lists its kinda risky to make it public aswell to collaborative.
How about making it so the author/user can give special privileges to others. Like it is with facebook-groups.
For example you can give another user full access to change whatever they want, or you could restrict the person to only have access too add new songs, and no deleting.
More and more people are asking for access to one of my playlist that I have collaborative with one other friend. But I don't trust others to not change anything, and therefore can't/will not share this with my other friends. Also you can't really trust it to be public when anyone can change your list.
This would make it possible to keep the list collaborative with the (trusted) friends and also give access to everyone else without jeopardizing the list(s).
If this is something you want, or just even think is a better way of solving the collaborative function - give it a KUDOS :)