Rust's async doesn't have this issue. Or at least, it's the same issue as malloc in an unbounded loop, but that's a more general issue not related to async or threading.

15-20 thousand futures would be trivial. 15-20 thousand goroutines, definitely not.

I don't know enough about rust to confirm or deny that -- but unless rust somehow puts a limit on in-flight async operations, I don't see how it would help.

The problem is not resource usage in go. The problem is that they created umpteen thousand TCP connections, which is going to kill things regardless of the language.