It would be nice if you have the abilty to add layers into the diagram. For example; if I have two versions of the diagram I would like to click on a button to see version 1 and than click on a button to see version 2 in the same diagram to compare the changes.
I was thinking something similar. I thought it would be nice to have Tabs (or pages). So you can click over to a different view of your diagram or to a related diagram. Layers could work in a similar fashion.