There appear to be several questions in the forum related to multiple libraries and multiple user functionality for Sonos. Most are currently marked as answered through work arounds or explanations on why this functionality is not currently available. I would like to put forward this topic as an idea so it can be up voted and tracked.
Sonos is a brilliant system, however in homes with multiple listeners who wish to maintain separate music libraries and services there is no specific functionality. Viewing by folder is not an option for people who carefully manage their music library through valid metadata and other methods to ensure proper music organisation which is broken by folder based viewing.
If multiple libraries were added then then when browsing music 'Music Library' could be replaced by one or more named libraries (which in turn would collect potentially a number of shares).
Multiple users with separate music service accounts, libraries and permitted zones would be the ideal extension of this concept but for many users I think just multiple libraries would be a big step in the right direction. All of these ideas should be implemented in a way that doesn't change the existing system if you only have a single user/library so the complexity only affects those who want to use it.
A big part of making a system like Sonos a success in a household (and therefore encouraging more zones) is more people in the household taking advantage of the system. The current constraints make it much more difficult to convince others in the household to use the same system in their own rooms, causing fragmentation with other users getting independent systems.
Music services serve as a great means of tracking listening habits for building playlists and music selection, having these tied to a single account for a entire household also limits their value in this respect.
Would like to see if others in the community feel these features are also important to have and show Sonos if this demand exists.