Browsers catching up won't be the end of transpilers. If you want to write modern JS and have it support old Android phones or safari, you're stuck transpiling. And, browsers well never catch up, there will always be new features to be trying. It's really beautiful: we get to try different possible future versions of JS and make an informed decision on what and what not to bring into the language.

Also I have a feeling we'll be seeing a lot more to-JS languages, not to mention apps written in Rust, etc that target webassembly.