New addition to the OP.
As a byproduct of building my own static busybox compiles in all supported Android architectures for my latest AIK-mobile v2.0
package I figured I might as well offer them up separately as well since there aren't any providers making Android x64 builds, at least not for all of them when I went hunting (to try and save myself some time). The installer detects what architecture (ARM/ARM64, x86/x86_64, MIPS/MIPS64) your device uses and installs the correct busybox binary to /system/xbin accordingly; it detects and supports "systemless" root installation as well, installing to /su/(x)
bin instead. It then cleans up any symlinks from a possible previous installation at that location and cleverly generates new symlinks directly from the output of the installed binary, so they always match.
My busybox configs and patches are available here: https://github.com/osm0sis/android-busybox-ndk
I've got a patch submitted to the official busybox mailinglist to resolve some API 21 compatibility, so that will probably be added in a future version to save people time and make it easier for more providers. Anyway, hopefully I got all the applets most people want working.
Now the zip will also clean up an installation made to /su/bin and then install to /su/xbin.
Edit 2: New special zip features
You may add keywords to zip filename or in a file at /data/.busybox-ndk:
system or System or SYSTEM to force a system installation.
uninstall or Uninstall or UNINSTALL to uninstall busybox from the zip's detected target location (/su/xbin > /magisk/busybox-ndk/system/xbin > /data/adb/su/xbin > /data/adb/modules/busybox-ndk/system/xbin > /system/xbin, unless system forced per above).
nolinks or NoLinks or NOLINKS to opt out of symlink creation and only push the busybox binary.
noselinux or NoSELinux or NOSELINUX to force the non-SELinux busybox binary to be installed.
For those curious, I automate bundling my busybox binaries directly with builds from my AIK Build Farm
using the following script.