I'm wondering why you exactly decided to go this route? I was expecting your app to be very graphically intensive or have some other kind of demanding requirements. When I went to the site it appears it's some kind of collaborative design tool? Not saying these tools don't require a top-notch UI. Maybe for manipulating and scrolling/scaling huge canvases? Coming from a mapping background, I can totally see this as something lacking in the browser. There aren't many primitives for creating these kinds of image-based interfaces.
There's certainly a trade-off between having super-fast performance and a completely custom rendering engine and adopting a not-often used delivery mechanism and stack (C++/asm.js). I'd imagine it's hard to find people who have all that expertise, it's hard enough finding a good frontend dev in the conventional technologies of the web.
Good luck on your product launch, can't wait to use your UI and play around with it.