We use WASM today and it's not for any performance reasons. Hopefully, like you say that will become an advantage too down the road as WASM matures. But, simply, there are parts of our application which we feel much more comfortable with and we find much more manageable being implemented in Rust and compiled to WASM. So for us WASM grants portability and language choice in a first class manner (as opposed to transpiling to and from JS and all the glue that entails). It's a real shot at dismantling the browser JS hegemony.