Why this

If you want to install Archlinux on ZFS, you need to deal with ZFS licensing problem. Kernel module isn't included in default archiso, you need to include it in a custom archiso to be able to install ZFS.

I wrote an article about archiso netbooting.
This project let you include zfs kernel module on any archiso without creating a custom one.

Archzfs

Archzfs unofficial user repository allows one to install ZFS kernel module in multiple ways.
We will compile current kernel zfs module using DKMS method. DKMS needs linux-headers of the currently booted system to be able to build the module.

How does it work

It uses Arch Linux Archive, to be able to install linux-headers required by DKMS.

How to use

Boot on any archiso, and use

curl -s https://eoli3n.github.io/archzfs/init | bash

This is a mirror with an easier url. Instead you can use a more hacky way

Wow, that's slow...

Yes, Arch Linux Archive have a limited brandwidth, but at least, it is automated. A better solution would be to store archives on Archzfs repo. More details here : https://github.com/archzfs/archzfs/issues/337