I feel this is quite a nuanced question, I can answer one aspect of it though. When I think of what 'memory-safety' means in this context I think mainly of buff

I feel this is quite a nuanced question, I can answer one aspect of it though. When I think of what 'memory-safety' means in this context I think mainly of buffer overflows, dangling pointers, etc, things that have nothing really to do with memory mapped IO. I can't speak for Rust, but I've recently been doing quite a bit of embedded development in Ada ( Disclaimer: Not an expert ) and it supports mapping variables onto a arbitrary memory addresses through a variety of means that don't forgo static typing and compile-time checking. You can use access-types which are the closest thing to C's pointers, they allow for direct memory access while still preventing a good deal of the issues arising from misuse of pointers. I'd say it's well worth checking out for yourself.