Systems programming in a memory safe language with automatic memory management, across the whole OS, with a type safe ABI supporting dynamic loading, as starting point.
Swift is the closest to it, and it is still not widely adopted across Apple ecosystem, although as per CppCon 2023's Apple talk they even have plans to push it into the kernel (long term).
"Across the whole OS" is nothing special, it just means there hasn't been enough interest by diverse enough users of the OS. This is a research system, which is different from an OS supporting a huge diversity of ecosystems through the past 3 decades or so. There are different forces at play.
I'm sure there are quite a few systems worked on by lone developers today that make for a nice and smooth demo. The hard part is getting adoption and making it ergonomic and performant for a variety of uses, not just demo stuff.
Swift is the closest to it, and it is still not widely adopted across Apple ecosystem, although as per CppCon 2023's Apple talk they even have plans to push it into the kernel (long term).