Nice! Really beautiful app and it works quite smoothly. 
I especially like that you can start from scratch and build up the graph with only the tables which you are interested in. In some other tools it’s always quite an info dump.
Speaking of other tools: If you haven’t yet, you should check out Salesforce’ Schema Builder, there might be a few features to steal. 
Is there any chance that you extract your graph rendering code into an extra package? I’m planing to build something similar and a graph rendering library would be a great starting point. 