I'll be the first to say, I wouldn't know how this would work coding-wise or if it would even be possible with Roll20's system, but : I think the idea of drawn barriers for Dynamic Lighting having two 'sides' could be useful. It would help emulate something like two-way glass, where from one side the players can just see a solid wall, but from the other they can see out to the other side. Ideally this would be something that could be toggled and would have some sort of identifier to let you know which side was which as you were drawing it.
