RFC: Shelf for keyboard-accessible file operations

[Dave Ahlswede <mightyquinn letterboxes org>]

I've read in the past that the Nextstep file manager, instead of using
cut/copy/paste to manage files without dragging, had a sort of virtual
folder called the Shelf that would temporarily hold files. To me, this
seems more intuitive than the current system. 

Internally, I think this could be handled much as it is now, except
there would need to be some sort of visualization-- in browser mode,
perhaps a sidebar, but a separate window in Spatial mode, with some way
of indicating to the user that it's not a regular window-- I'd propose
the icons be drawn translucently to indicate that they're "shadows" of
the real files, and would have a context menu item that would open their
parent folder.

The statusbar of the window would read "X files on shelf (Y MB)", and
have no parent folder dropbox. Closing the shelf window would empty it
without performing any real action on the contained files, with a
possible warning stating this. "Deleting" a file on the shelf would
cause the same effect-- the original file is left alone and simply
removed from the shelf.

Context menus would have "copy to shelf" and "move to shelf" options
that would function much as copy and cut do now, but there would be two
potential paste actions, a "put all files from shelf here", and if
applicable a "put selected files from shelf here".

Incidentally, if this were exported in a public way, it might provide an
accessible version of drag/drop saving, should that be implemented--
simply "save file to shelf"