No, layout is all CSS with some JS mixed in, and will be for a long time. Webassembly will help accelerate heavy mathematical computations such as canvas graphics.
You could hypothetically use Webassembly to build your entire application around a canvas and either render directly with canvas calls or WebGL, but it would somewhat miss the point of the web unless you're explicitly building a game or something.
This is what Figma is doing for their main UI, they reimplemented everything [1]