There's a limit to what can be done with the current structure - all the
drawing takes place on the server, so any change requires a roundtrip to
the server, and the encoding of a new PNG file (which can take a little
time) and sending it (which does too). I did actually have something to
do some of this as a demo, but it's really hacky, and hasn't been
updated in years. I made video of it, back in 2009 or so:
https://youtu.be/0UPiBKLi4fI
The funny delays aren't a problem with the video - that's the server
roundtrip still happening to update the links when nodes are let go
after being dragged. So the actual speed isn't really faster, but it
feels more interactive.
However, I'm not planning to pursue that in favour of the long-term plan
which is to move to SVG, generated on the client, which opens up a lot
of possibilities both for the editor, and for things like realtime data
updates (or different-frequency updates).