> Why? If WASM has access to the DOM, and it's competitive in terms of performance - why would JS still by the goto? At that point, people will just choose whatever language they want, I don't see JS having an advantage there any longer.

Because of the built-in garbage collector, only non-garbage collector languages will actually be faster on WASM (so not that many of them) and the JS ecosystem is already so big that you would need a lot of work to match it in its current state.