Yeah I'm somewhat familiar with getting rust bootstrapped, I still have the 15/16/17 rust toolchains built for mipsel kicking around. Worst part of that was targeting wheezy though.

It just seems odd that these architectures seem to have official rust support but are being problematic on Alpine. Self-hosting might be a sticking point, but seems a bit of a silly one given how slow some of those architectures are.

When bootstrapping a new arch, you usually cross-compile to get it working. This means that you don't need to build all of those builds. If you want to start a new bootstrap chain, which is what most distros have done, you do this once and then go from there as new releases come out.