What you can do with WebAssembly regarding front-end development is running your Qt/GTK+ type of programs on web.
But noone is interested in that. As a matter of fact, current trend seems to be ditching that sort of program on desktops and using HTML/JS/CSS stack for desktops as well (atom, slack, etc) because its much easier to create a top-notch UX using HTML stack.
HTML stack is very resilient. It evolves at a fast pace. Don't underestimate it.
WebAssembly will definitely have its own use case in the future (games, apps with specific performance requirements) but its not replacing frontend development.
Regarding backend, its not going away. Serverless doesn't mean backend-less. It means backend deployed in a very distributed fashion.
I personally think backends will be thinner and thinner as databases gain more responsibility an functionality.