Is it not a bit of a paradox that said embedded platforms matter enormously right up to, but not including the point of having toolchains ported to them and maintained? And yes while gcc can be built to produce binaries for an alpha it's not producing any bugs right?

The interests of people writing new language toolchains sadly does not seem to extend to supporting older platforms. This doesn't mean that they are not important, it just means that that they are not important to the people writing the new language toolchains.

It's not a matter of interest; if an embedded platform matters they should be willing to pay someone to port Rust.

…or they can just continue using C.

And not be surprised when open source maintainers don't go out of their way to continue supporting their poorly supported platform...

There are a few niche embedded targets that Rust might not have a toolchain for, but the vast majority are actually well covered. MIPS, PowerPC, the relevant flavours of ARM, MSP430, RISC-V.