A nice drawing feature would be when you click to start drawing, if the object you click on is in the same layer, the line would auto center.
You wouldn't always want this but it would be nice when you are continuing a line.
Another feature that would be nice is if you start drawing with a new layer, and your first click is on a different layer, you could automatically "bond" to the other layer.
What I mean by this is if I start drawing some metal2 on top of metal1, I could have a via automatically generated.
I am not sure these can be implemented with the ruby extension currently as I don't think it can intercept mouse clicks yet.