If you go ahead and allow multiple panel choices, all sorts of magic is possible. To support this in Panopoly we need:
-- The patch from #1790434: Panelizer panel select tab (activated with 'allow panel choice') not appearing when adding a node.
-- Updating Panopoly Admin to have the selection box show up cleanly on the admin page
-- Make sure that reverting correctly goes back to the selected default
-- Figure out the deal with "Access" options there