That's a really dumb thing to say.
Btw, WebAssembly has nothing to do with choice, but with performance, its primary purpose being to let C/C++ to run in the browser. And was preceded by Asm.js.
This is actually very relevant. Going with WebAssembly means you're going low level — e.g. a language author will no longer have the JavaScript runtime to piggyback on, no garbage collector for example. Which might be good news for a language like Haskell, because people now have the opportunity to run the actual GHC runtime and garbage collector in the browser. But you have to port it all and the binary size downloaded by users will have to include everything.
So language implementations like Scala.js or PureScript aren't rushing to WebAssembly yet. In the future anything is possible of course, but currently it's not a useful compilation target for garbage collected languages.
Therefore I don't have good news — if diversity is what you're looking for, then know that WebAssembly was built for C/C++ and Rust and languages not fitting this narrow profile are out.