I'd also like to see the smallest Rust binaries that are achieved by real projects. When the most size-conscious users use Rust to solve real problems, what is the result?
Yeah, so, using arm-none-eabi-size, one of these apps I have built, the total image size is 74376 bytes. The kernel itself is 29232 of those, the rest are various tasks. RCC driver is 4616, USART driver is 6228.
We have to care about binary size, but we also don't have to stress about it. There are some things we could do to make sizes get even smaller, but there's no reason to go to that effort at the moment. We have the luxury of being on full 32-bit environments, so while there isn't a ton of space by say, desktop or phone standards, it's also a bit bigger than something like a PIC.
Lots of folks also seem to get the impression that Rust binary sizes are bigger than they are because they use ls instead of size; we care deeply about debugging, and so the individual tasks are built with debug information. ls reports that rcc driver is 181kb, but that's not representative of what actually ends up being flashed. You can see a similar effect with desktop Rust software by running strip on the binaries, you'll often save a ton of size from doing that.