There is nothing in the File Picker that informs a screen reader user of which repository is currently selected. None of the repository links are read as selected by a screen reader, and there is no heading, title, or breadcrumb that would indicate the currently displayed repository. The only way for a screen reader user to know which repository they are in is to select a different repository.
A video demonstrating this issue can be found here: http://youtu.be/uPcdgVgKI_I
Steps for testing:
1. Enable JAWS or another screen reader and open the file picker.
2. Press CTRL+Home or set focus to the top of the file picker modal.
3. Press Insert+DownArrow or use the screen reader's "say all" feature to read the entire File Picker modal.
4. Note there is no announcement at any point of which repository is currently displayed. Note that none of the repository links is read as "selected" by the screen reader.