It's already happening isn't it? When WebAssembly gets direct DOM access, there will be many contenders to JavaScript's throne, e.g. Rust or some superset of AssemblyScript. Perhaps TypeScript will eventually transpile directly to WebAssembly.
Well I'm reading between the lines a bit, but one of the WebAssembly high-level goals [1] is to "access browser functionality through the same Web APIs that are accessible to JavaScript" and "Once GC is supported, WebAssembly code would be able to reference and access JavaScript, DOM, and general WebIDL-defined objects."
