You know what would be a great workflow, it just occurred to me?
You'd select all, then do EXPORT > AUDIO, and
then you'd get some sort of version of the navigation view in a dialog box, where you could set your start and end points. Sonar could do a best guess, but let you change it if it was wrong. And it could keep the settings as part of the project, so it's just a click-through if it's already right.
The current system works fine, once you're used to it, but it's really error prone. Like accidentally selecting all if the last thing you did was on a bus, you end up selecting no audio. I think deriving the export range wholly from the standard selection paradigm is a bit messy.