Yeah, I was going to raise that. There's no guarantee that ObjectiveC and Rust's unwinding mechanisms are related in the slightest, and if you are on a platform where a de facto guarantee does exist, then you probably know how to catch exceptions from the former.
I would like similar abilities, but what is probably needed is a way to directly interact with the unwinding mechanism (SEH on windows, Sys-V/Itanium Unwinding, etc.), which would probably need to be platform-specific.