When I made the first version 2 years ago I thought that classes would feel more natural to newbies, but since then have data-attributes become pretty much standard in the community.
But today it's mostly a performance thing. List.js is supposed to be very fast and handle really long lists (check out http://sindresorhus.com/bower-components/ it has 6000+ items)
With the new plugins-functionality you could create your own special sorter that uses data attributes too. Then you would call it with listObj.yourSortersName(something).
And you can still use the regular sort function which since this version is a included in the helper object :)
Actually I realized I can already do this even without plugin functionality. The Item object passed to the sorter has access to the element http://screencast.com/t/Z5uVYNtH8
With plugins you can build your own fuzzy search! :)
...but I know that is a feature many want, so maybe I will build a plugin if no one get before me.