The criteria for additions to the standard library have been officially stated, yes. See John's acceptance post for SE-0255 for a recent example.
Now these things are subjective. One person's trivial sugar is another's major readability improvement. But I don't think it's credible to argue this is a key improvement for fluency, and it certainly doesn't match criteria such as "complex, challenging, or error-prone for users to implement themselves" or "have substantial performance advantages over a user implementation".