I'm only about a third of the way through the rust manual myself, so I can't say with confidence, but I suspect that rust's safe memory abstractions don't necessarily scale down to the lowest end of MCUs. The machine code instructions that make the code efficient simply may not exist on an 8-bit segmented memory CPU. That also touches on the gaps in LLVM support. I'll bet it's perfectly viable these days on any cortex-m MCU, though.
Also, a lot of embedded code consists of peripheral drivers, and in rust that likely means "unsafe" code. At that point, it's a bit of a wash which language you work in. That's especially true since rust can interoperate with the C ABI.
I haven't familiarized myself with all of rust's built-in data structures yet, and I'm not sure how much stuff necessitates allocating on a heap under the hood. That would be a compelling reason to carefully consider its use in some embedded systems. That's analogous to C++, where it's typical to avoid most of the STL data structures.
Most of Rust's memory safety comes from compile-time checks, not runtime code.
You do need some unsafe, but not as much as you may assume at first.
Rust doesn't really have any complex built-in data structures, and doesn't require a heap at all. That's a standard library thing, which you wouldn't be using in this context.
Also, a lot of embedded code consists of peripheral drivers, and in rust that likely means "unsafe" code. At that point, it's a bit of a wash which language you work in. That's especially true since rust can interoperate with the C ABI.
I haven't familiarized myself with all of rust's built-in data structures yet, and I'm not sure how much stuff necessitates allocating on a heap under the hood. That would be a compelling reason to carefully consider its use in some embedded systems. That's analogous to C++, where it's typical to avoid most of the STL data structures.