Right now we have two tools that allow us to show things only to specific people, invisibility and images passed directly to a client.

Being able to specifically choose if something should be drawn on specific player's screens according to specific parameters would help a lot with multi-floor isometric maps and things like that.

I would conceptualize a simple truth check that could perhaps be calculated client side, but even if it was only server side it'd be desirable over creating images for everything.