No, it's a fail if every website renders itself to the canvas. I think there's a middle ground where, for example, unknown mime/image types can be handed by "application level"--actually middleware or library-level--codecs supplied as Wasm extensions. The browser doesn't have to ship with them, and it doesn't have to trust them the way it does plugins, but they can hook into key places in ways that maximizes the benefit of having a rendering/layout engine, yet is extensible, fast, and secure.