Some more random thoughts:

** If you are going to use a group I wouldn't use "usershare" only because there is a Samba thing called usershare. There already exists a group you can use call plugdev. Once upon a time during the "Golden Age" of Linux all new users were automatically made members of the plugdev group but now you have to add them manually.

** Creating a shared partition as NTFS will in fact work just as Paddy Landau indicated as long as you have it mount automatically. In fact one way of looking at bindfs is that you are doing to a Linux partition what ntfs does by default. Creating an view of a partition or folder with immutable permissions.