There has been very good progress on filling in the gaps to officially get Rust's AArch64 Linux toolchain triple to Tier-1 this year. We have CI for the Rust compiler test suites on native AArch64 silicon in a joint collaboration between Arm and the Rust lang core team and are converging on zero compiler test failures. Overall, we are pretty close to attaining Tier-1!
We haven't been very vocal about it just yet but all the bits to enable CI etc and the new t/compiler-arm Zulip stream are happening openly pretty much.
I'll be pinging all the relevant folks soon-ish (we're pushing out fixes to the last remaining compiler test suite failures this week).