I'd love custom user-addable extra layers which can be toggled visible / hidden. When hidden, a layer is invisible to players and only visible to GM if you are on that layer. Purpose -- to show / hide these sorts of things: roof layer of buildings the bottom of a crevasse invisible until you are on the edge change map features that only show up after an event -- lower the draw-bridge, clear the rubble, etc. It's too cluttered to have all this stuff on the GM layer, always displaying as ghosted. If there are multiple full storeys of a castle or dungeon, I think these still have to be laid out in 2D as otherwise lighting and having players on different levels gets too complex.
