I recently learned that the AUR seems to have an actively enforced moderation policy preventing packages that either only work on aarch64, or are otherwise heavily focused/only useful on that platform.

RFC0032 hasn't finalized yet, and of course it could still end up being rejected or otherwise put on indefinite hiatus... My outsider perspective is that it likely will​ happen though, so I'm working under that assumption.

In this case, it's only a matter of time before non-x86 communities are accumulating around Arch upstream proper. RFC0032 already notes that:

I have a concrete proposal here. Let's say I (or someone else) were to contribute the necessary changes to aurweb, such that it exposed architecture info in the RPC (archlinux/aurweb#485), as well as adding support for filtering by architecture when searching. If this happened, and the search box on the AUR homepage defaulted to x86, would it be possible to relax the current moderation policy that restricts aarch64-only packages from living in the AUR?