Redox also has it's own non-standard shell that has been worked on for a while, called Ion. I don't believe it's entirely POSIX-compatible, and has some neat features of its own. That said, it's certainly possible someone could end up porting over Nushell to work on Redox, but I don't think that's currently on their roadmap.
The default shell is ion, a shell written in Rust and maintained as part of Redox. But I don't see it as important what the default is, so long as it is configurable.
We have ported bash and dash, so far. I think porting nushell wouldn't take much work