Legacy IE support is coming, as well as precompilation to CSS. Those will fix your concerns.
But on modern browsers GSS can already solve and lay things out in 60fps.
But on modern browsers GSS can already solve and lay things out in 60fps.
Also I believe that many problems that this is trying to solve is already alleviated in existing technologies that will work in modern browsers, including IE10+, and web documents do not necessarily need constraints.
I think contributing to Mozilla or Webkit, or proposing a specification to the W3C would be more advantageous for your cause.
As for performance, that sounds very dubious given that even my Nexus 7 does this thing at 60fps
Runs a bit smoother in Firefox.
Adding another slow layer is not really helping anything: by the time you have browser-C++-overhead + DOM overhead + JS interpretation/V8/SpiderMonkey overhead, adding another layer on top of this all is really not wanting to make me develop on this platform.