I've been giving thought lately to writing my own shell, because there's stuff I want to fix that no current shell does right, but job control is one of the big reasons why I haven't actually started writing code yet (namely, I haven't yet figured out how to reconcile the stuff I want to do with the need to let the user suspend or background tasks including shell scripts).
https://github.com/redox-os/ion
It's intially build with RedoxOS (in Rust as well) underneath, but now also runs on Linux. Seems to be a bit more mature.
I wonder what sets these two projects apart, and/or if the devs of Casada know of Ion's existence.