We just pushed a major update publicly yesterday that had some incredible performance gains (50 - 100x faster). We have also done a bunch of selective rendering updates which make it feel a ton faster to use.
You should give it a try again and let me know what you think! Hopefully we are a lot closer!
Most EDA software is written by companies who have no interest in letting you see how their proprietary formats work.
Oh boy, I know it, and it's been a pain in my side. However, EAGLE (lots of hobbiests use it) is migrating to a fully-documented XML-based format [1], and there are two open-source projects for schematic capture, kicad and geda, which would give someone a head start on parsing their design files, at least.
Other than that, this looks really awesome!
Diffing has been talked about internally and it would be pretty awesome.