[nbevans]

It's not so much about picking your "favourite" language. That's what drove NodeJS to exist. But more about picking a more appropriate language that has a well engineered base class library and third party libraries. They will come. This comes down to choosing the best tool for the job at hand.

JavaScript developers have been able to, in recent years, benefit in some ways by being able to write their server-side in JS as well (see NodeJS). There are various buzzwords to describe this capability. WebAssembly will help normalise this so that other languages can also have this capability. By being able to share types between the server and web browser client, there are large productivity and program correctness gains to be unlocked.

[bobajeff]

People are hyping up webassembly way too much. Don't get me wrong it's going to be awesome being able to compile C++ and C programs that run on the Web runtime.

But it's not going to be without it's own issues. For one developers will likely have to wait for things like simd, pthreads or 64bit ints until later versions.

Also it won't magically make compiling your language of choice to the web less painful unless it's C++ or it fits into the C++ language model. Even when it gets the ability to hook into a garbage collector (I wouldn't count on it happening any time in the near future) it will likely have to fit in with the way js engines expect.