Hacker News Reader

Every reasonable. Maybe I am wrong, but tco usually means no more stacktraces?

No, only dumb implementations, Scheme and other languages that require TCO have no issues mapping the debugging metadata to proper calls.

Not at all! Elixir stacktraces are much nicer than JavaScript ones.

stackful coroutines, an "await" keyword that only awaits one layer of awaitables instead of infinitely many layers, etc.

JavaScriptCore has tail calls

Nothing that one can rely on for portable code.