Unless you have a demo already - which would be awesome.
The github analogy is not very accurate because github was built on git and ruby-git bindings. Its a product play that was clearly understood. What I'm not able to understand is how you are planning to execute your product.
Please understand why I'm asking this - if you are claiming to integrate with an existing CAD server software ... then that is something that I would completely understand and go for. But I dont know if such a thing (with API bindings exists). We can also debate about how you will version these things - since AFAIK these kind of software dumps into a barely readable binary format.
The alternative is that you would invent your own a) CAD software b) javascript UI c) snapshot format. That makes me a bit uncomfortable... unless you already have atleast one of these three.
The question really is - how far along are you ? its a standard YC question.
EDIT: btw your demo looks very very similar to a Jupyter notebook. If that's the case, then the innovation you are making is actually a CAD software on top of Jupyter (which like git and github is a well known analogy). That would seriously simplify this conversation a LOT.