Hey, glad you are working on this. I have later given a talk on structural version control together with demos of structural editing and ydiff. Here are the slides:
I think structural version control can open lots of possibilities that are not accessible by text-base version control systems. I'm not really focused on this area, but I'd be happen to to see more people getting interested in this and work on it.
As for the performance of diffing, I think the bottleneck is with detection of moving. That's something that text-based diff doesn't do at all, so not a big drawback. But with structural editors, those moves can be instantly detected and logically merged by the editors. That's too far into the future though. But I think structural diffing without move detection can be of good use already.
Another direction that's possible to detecting moving more efficiently is to use hashing, the same trick used to eliminate redundant expressions in a compiler.