We're not aiming to replace the tools you already use, just make it easier to share your work on the web. I do love the idea of a web based EDA tool, but I'm yet to believe it can be done with performance characteristics that will work for any reasonably complex circuit.
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.
But I think they're coming at the wrong end. Their schematic capture was painfully slow when I tried it a couple weeks ago, and I (and I suspect nearly every other electrical designer) rues having to change tools. If someone wants to become the 'github of electronics', I strongly recommend working on getting some sensible versioning and sharing going without also tackling the problem of creating EDA tools.
Having said that, a shared crowdsourced library is a big help, and some others have already noticed the good it can provide: https://github.com/adafruit/Adafruit-Eagle-Library