Now, these sorts of systems should actually be _easier_, in the long-term, to build in Rust, since the type system can enable a class of proof which simply was not historically possible, but for the time being, the tooling doesn't exist yet.
I think the "safety" of "familiarity" vs pushing the envelope of what we can do technically are different things. We used to build brand new computers and operating systems from scratch specifically for these types of things.
The risks are indeed high for managerial staff. I worked at a large quasi-government place. "you won't ever get fired for using Microsoft, Oracle, etc" was a tagline we heard often in non-critical systems, so I imagine there would need to be some major technical reason to switch.
Now drones on the other hand... https://en.wikipedia.org/wiki/Iran%E2%80%93U.S._RQ-170_incid...
people were writing mission-critical C++ when C++ was new / only a few years old; with this in mind, rust is probably good to go with sufficient application/system testing
that said, since C++ & associated tooling exists, there is more of an opportunity cost since, in the context of today, there are more alternatives that could be considered
There should be an industry push for certified Rust tooling, it would save the aerospace and auto industry billions. Or you could use the unsexy but also very good ADA 2012, which is already certified.
I suppose the workflow would be to flesh out and check the abstract design in something like Coq or (maybe) TLAPS, generate a refinement into the SPARK code contracts, then implement the functions. Since the toolchains are verified there shouldn't be much surface area for bugs left.
"Building High Integrity Applications with SPARK"
https://www.amazon.com/Building-High-Integrity-Applications-...
"Building Parallel, Embedded, and Real-Time Applications with Ada"
https://www.amazon.com/Building-Parallel-Embedded-Real-Time-...
"Embedded Software Development for Safety-Critical Systems"
https://www.amazon.com/Embedded-Software-Development-Safety-...
Rust almost certainly could do the job now but stakes are so high no one would take that risk when its proven that C can do it and with enough auditing and conservatism, it can be done pretty safely.