I don't know. I use a lot of Swift and C++ and while both are OK languages there is an absurd amount of complexity in these languages that doesn't seem to serve any real purpose. Just a lot of foot traps, really.
Coming back to Plan9 from that world is a breeze, the simplicity is like a therapy for me. So enjoyable.
If "modern" means complex, I don't think it fits Plan9.
AFAIK there is no Rust compiler for Plan 9 or 9front. The project is using a dialect of C and its own C compiler(s). I doubt adding Rust to the mix will help. For a research OS, C is a nice clean language and the Plan 9 dialect has a some niceties not found in standard C.
If you really want Rust, check this https://github.com/r9os/r9 it is Plan 9 reimplemented in Rust (no idea about the project quality):
R9 is a reimplementation of the plan9 kernel in Rust. It is not only inspired by but in many ways derived from the original Plan 9 source code.
ZeroFS [0] is very thankful for what it brought to Linux with the v9fs [1] subsystem which is very nice to work with (network native) compared to fuse :)
Which tends to be forgotten when praising Plan 9.
Two key design difference from Go and its two predecessors.
However the influence is quite clear, plus the Oberon-2 style methods and SYSTEM package.
Knowing that project am I going to be rickrolled?
If "modern" means complex, I don't think it fits Plan9.
If you really want Rust, check this https://github.com/r9os/r9 it is Plan 9 reimplemented in Rust (no idea about the project quality):
R9 is a reimplementation of the plan9 kernel in Rust. It is not only inspired by but in many ways derived from the original Plan 9 source code.
[0] https://github.com/Barre/ZeroFS
[1] https://docs.kernel.org/filesystems/9p.html