NSDocument is based on the data stored in the data fork of a file. Could it be modified to work with xattrs instead? And dipping my toes into NSTableView.
xattred
This tool now has an overhauled interface, making it much easier to use. Currently the only way of viewing and editing xattrs without using the command line.
Using wrappers to call C functions which give direct access to xattrs, handling throws, and converting arbitrary Data to Strings.
A free tool to force full Gatekeeper checks without having to download an app, inspect, add, and remove xattrs from files and folders.
The Eclectic Light Company 