Currently dealing with a zfs cachefile issue on my nas, where hrmpf has been instrumental in letting me backup data and regenerate a cachefile from my macbook.

That is really useful. Having to build an archiso every time I accidentally pacman to a kernel version that breaks zfs is annoying. I’ve only done it twice but still.

Why not just build once and then keep the USB for emergencies?

I mean I do keep them but they get too old eventually and then they won’t mount the pool, or will only mount it read-only.

Both ZFS updates and pacman breaking are rare enough that I forgot that would happen. Though using this rescue system would work, there's also a group that maintains a script to grab the correct ZFS module for a running archiso, might come in handy for you.

https://github.com/eoli3n/archiso-zfs