i wait until they come to the hard stuff like awk, sed and grep.
I don't know of a sed equivalent, but I guess that would be easy to implement as Rust has good regex support (see ripgrep), and 90%+ of sed usage is search-and-replace. The other commands don't look hard to implement and because they are not used as much, optimizing these is less of a priority.
I don't know about awk, it is a full programming language, but I guess it is far from an impossible task to implement.
Now the real hard part is making a true, bug-for-bug compatible replacement of the GNU version of these tools, but while good to have, it is not strictly necessary. For example, Busybox is very popular, maybe even more so than GNU in terms of number of devices, and it has its own (likely simplified) version of grep, sed and awk.