By most accounts the Rust4Linux project has made the kernel less complex by forcing some technical debt to be addressed and bad APIs to be improved.

The Linux kernel is already very complex, and I expect that replacing much or all of it with Rust code will be good for making it more tractable to understand. Because you can represent complex states with more sophisticated types than in C, if nothing else.

Complexity of Rust is just codifying existing complexity.

There’s one already — they seem to be doing decently well.

https://www.redox-os.org/