Well, best might add those things in the future but what you are talking about would require uber amounts of time and energy spent on making images, placing constraints so that you can't build buildings halfway off a cliff, making sure that each building svg rendered on a cliff is offset by a degree of y, etc. etc.

If you want this in the game, start by developing textures for the cliffs that would fit into the game nicely so bast doesn't have to.