Thanks @Calabar I will definitely prepare a proper post :)
The viewer actually reads LDraw files, but any software has to parse them into its own internal display format. In this case, our viewer uses webGL, based on a library called Three.js.
With the tests we did (mostly using .LDR and .MPD files of official builds found online, namely here on eurobricks) I would say 95% of all parts are opening nicely and correctly placed, the only parts missing would be non-official parts we haven't added yet, but all it just ignores those. So please feel free to test more models. The largest model we tried is the Millenium Falcon (10179).
The viewer also converts into a format that can open in our main product, the 3D MakerSpace. Think of it as a "Universal Digital Designer", it isn't LEGO specific, and wasn't meant to to have all the LEGO parts, just a subset compatible with our own physical product called Branes. But then our Branes themselves changed and became compatible with more LEGO parts, and the MakerSpace started to be used by all kinds of users including pure LEGO fans. So we figured why not add as many parts as possible since the LDraw library is there.
But in the case of the builder, it was easier to convert them to a non-LDraw format for coherence with the non-Lego parts we already had on the platform, and we're making them gradually available in the 3D MakerSpace.
You didn't sign an NDA? ;)
The 3D MakerSpace is a very different building style and interface than Mecabrick's manual+grid snap.
It's exponentially more difficult to solve for multiple systems and parts on non-standard grids and do drag and drop (continuous rendering) and autosnapping, especially that in the browser you have much less access to raw power like a native app (eg. LDD or stud.io) do. But we made it work! While we tweak the performance, it's in Beta at http://makerbrane.com/makerspace.