IME Lambda functions are mostly sitting around waiting on I/O, so I don't think it would make much of a difference for those workloads. The important technical factors for those workloads are startup time and I/O capabilities...JS is strong in both of those areas. For simple Lambda functions JS still seems like a great choice, along with Go. Rust would be overkill IMO unless you need to share a codebase or aren't I/O bound or have some other unique requirements.