Global Priority Ranking across all Themes

According to all I've read about Scrum, having one globaly ranked backlog is key. While I like ordering the User stories into Themes for clarities sake, It makes the absolute ranking of the backlog a task that needs to be done ouside of your great app. Any chance this is a feature you are working on? I could use only one theme to have a global rank, but that also would name all my user stories like the one theme which wouldn't be very helpful too.