I think it would be nice to expand folders in a tree view in the
folder pane while in list view mode, like in Nautilus list view.

Expanding trees in the side pane is useful to find folders, but
you can't see files in there.

Sometimes in a complex directory structure I can't remember where
I put a particular file.  It's nice to be able to expand folders
in a tree view below the currently open folder in the folder pane,
to see all the files and to be able to move files to other folders.

Thanks.
Mark