I'm a big fan of Rust on embedded (and think embassy in particular is awesome, haven't tried this Ariel OS.)

I would say however that there's still toolchain issues here. There all kinds of MCUs that simply don't/won't have a viable compiler toolchain that would support Rust.

e.g. I recently came from a job where they built their own camera board around an older platform because it offered a compelling bundle of features (USB peripheral support and MIPI interface mainly). We were stuck with C/C++ as the toolchain there, as there was no reasonable way to make this work with Rust as it was a much older ARM ISA