Quite contrary to what most seem to believe I'd say wasm will only strengthen javascript. At the end of the day most of the web will still use js, most libraries around "web'y" stuff will be js and wasm will help js overcome some of the performance limitations (and  js VMs are already performant as far as dynamic languages go). Many of the wasm libraries will probably be designed with js-interop in mind. So while technically it may be easier than ever to use whatever you want to write your web thing I don't think many will for real projects.