https://www.redox-os.org/ Redox is a super interesting project. Not because it’s Rust based. But because rarely do people start from scratch to build a new OS. (eg, OpenBSD forked NetBSD, Dragonly forked FreeBSD, Ubuntu from Debian, etc) —- https://fuchsia.dev/ Would be another of interest.
The most innovative concepts historically would be Plan9, BeOS, and seL4.
Plan9's approach of "everything is a file" is something that was unique.
BeOS's extensive use of journalling and metadata in the filesystem gave it big advantages.
seL4 being the most rigorous application of a micro-kernel architecture, and making use of formal verification make this one stand out.
Capability-based operating systems also offer immense benefits.
Fuchsia and Redox are clearly drawing some inspiration from these. Along with GNU Hurd, which you didn't mention.
As for shells, nushell is clearly revolutionary. Something that points to what a better world might have been.
I would also recommend looking at Lennart Poettering's vision that extends on innovations like cgroups, journalling filesystems, ostree, etc.
https://0pointer.net/blog/projects/stateless.html
And of course, Nix and Guix both align with this vision of reproducibility, statelessness, and transactionality... along with Fedora Silverblue.
I kinda think of this as making the filesystem work more like git. A distro is a branch. A rollback is a branch from a previous commit.
And then the build system would be completely idempotent... every compilation from any system would be byte-for-byte identical, and thus verifiable in a security sense. And every upgrade on any system could be undone.