In my export plugin I need to know which directory the user selected in the directory browser while he was in the library module (or the name of the collection in case he selected a collection instead of a directory).
Mmm ... I wouldn't say the SDK is unaware of collections "by design," but by necessary pragmatism. There's no shortage whatsoever of excellent ideas for SDK additions :), so every version entails making some difficult choices. Our choices so far have been weighted toward what we thought would best support export extensions.