When you read about Web Assembly, you can read about all the high performance languages you now can run in the browser. Never the less, I have to show you now four limitations, that you should consider before migrating to your favorite ‘high performance language’.
Second: You still have the limitation on the JS VM. You only have a single threat. Your favorite language might support multi threats. On the browser you are still limited to a single treat. asynchronous processing with golang will not run concurrently on multiple CPU. At this point, I have a wish. Please enable Web Assembly to work with the new shared memory buffers. This could enable compilers to produce code, that is creating multiple WebWorker, they all could access the shared memory.
Fourth: Access the DOM. To build web applications you have to manipulate the DOM. the DOM is not available directly in WASM. Some API wrapper will be needed. You could try to draw you app entirely on a canvas. As of today, I do not believe you can gain performance advantages, that are worth the extra effort.
So, here you have it, do you still want to use WebAssembly? The plain Advantages of other languages still apply. Static typing, fast-ish memory access compiler optimizations and all the plugins and features of your favorite IDE.