Eg once upon a time I thought it would be fun to add a flag to ls to limit its results to a certain kind of file so you could list only directories for example. It came up for me as something I needed so I did it. Somebody on the gnu mailing list for core utils rejected it on the basis of ls "having a high bar" for a new flag. $ man ls suggests this hasn't been a consistent policy. It wasn't clear to me if that person was in charge or it was just a vague notion of theirs or anything useful so obviously I dropped it because I'd have something different from someone if there was any interest.
The Rust implementation might come to precisely the same conclusion that it isn't worthwhile. But they also might not on some case if not that one.
Do they do what's better or do they do what's Gnu always and everywhere?
Do they wait until they have significant traction and only then consider such things?
Interesting questions for them to ponder and maybe they have?