With the attached patches it is possible to build busybox static with an extended mount, which can mount by label. This would allow us to drop nash and use busybox for the initrd.
Created attachment 100659 [details] specfile patch
Created attachment 100660 [details] patch to mount by label
Created attachment 100661 [details] the .config for busybox to build busybox-initrd
FWIW, I'd rather look at making it so that there's only one busybox binary instead of three. Having it static definitely makes sense and I can't see a convincing reason to have completely different config sets.
static is the key, as the other configurations haven't been static! Beware of glibc getuid() and friends. They need the dynamic .so's at runtime (nsswitch.conf).
Busy box is now build static