> more stable (if near-abandoned) pastures of Standard ML

There's dozens of us! Hundreds maybe! It's not abandoned. It's more like with Lisp where the language is complete. Almost perfect as-is. Nothing left to take away and nothing left to add. Except Unicode and record update syntax.

The deciding factor for my personal projects was that SML is the exact same language it was 30 years ago. And it will be in 30 years. Though if you stick to Haskell 98/2010 it is similarly stable.

Speaking of SML and functional languages in the browser, MLton has a WASM target now: http://mlton.org/RunningOnWASI