I'd imagine one of those killer features is using a language with a solid standard library. Npm dependencies are notoriously complex because js as a language is missing basic functionality that is standard in other languages. Just a few years ago the Internet broke because "pad left" was pulled by it's maintainer, that simply doesn't happen in other languages

From a maintenance perspective npm is a nightmare. From a security perspective it is worse. Being able to build your entire website using a language that eliminates most dependencies, and the ones you take on don't pull in a zillion dependencies either, is absolutely a killer feature

Of course that isn't the full story and using js still has it's advantages as people have already pointed out. If wasm closes the gap in those areas then it would absolutely be worth the switch