Your post doesn't address the point that many of these "write a new operating system in my favorite language X" projects have great pedagogical value to the ind

Your post doesn't address the point that many of these "write a new operating system in my favorite language X" projects have great pedagogical value to the individual developing them. I've done plenty of experimentation in this area and I harbor no illusions that my efforts will ever be adopted into the mainstream. Operating-system development is an extremely broad and deep area of study. Writing toy operating-systems remains the best and most fulfilling way to learn. While I can't speak for D, Rust, etc, I can speak for what Ada can offer the field. Ada, and especially its formally verifiable subset SPARK are languages designed with secure and maintainable development in mind. I think there's tremendous value in continuing research into the formal verification of operating-systems. SPARK is a much better option for this purpose than many of the other languages available.