I was going to give the example of X Window System and TeX as official graphical interface and typesetter, yet less GNU and not managed by GNU ^^ They’re not GNU packages.
The maintaining rules you quoted apply to maintainers as individual and per their opinions and thoughts. Yet, there is a *mandatory* requirement on GNU software not to advertise proprietary software, not to use refused terms such as “Linux” for the GNU/Linux operating system, “open source”, “cloud”, etc.
