As far as I know, bug-libunistring is still intended to exist independent of gnulib. At least I have never heard otherwise from Bruno.
However, Bruno has just today officially stepped down as maintainer of libunistring, and all his other remaining packages. Daiki, would you like to become the new maintainer? Alternatively, if you think libunistring as a separate entity should go away and it just be part of gnulib, that's fine. Ditto libiconv (another of Bruno's packages), which I suspect is in a similar situation, on both counts. karl