> Better still, a lot of these languages are coming to the browser (via WASM or transpilation)
I think this has always been a concern - CoffeeScript had its moment in the sun, then the good parts got merged into JS and it died out. We'll see if that happens again.
WASM concerns me, though, because of the utility you outline, which doesn't actually serve the end-user in any way shape, or form. Much like we're seeing tiny webapps made with React (and requiring browsers to download and parse the accompanying runtime), I worry we're going to see sites using e.g. Kotlin in WASM simply because that's the developer preference, totally ignoring the fact that it means every user is going to have to download a Kotlin runtime and garbage collector despite there being a perfectly good JavaScript one sitting right there.