Why this

If you want to install Archlinux on ZFS, you need to deal with ZFS licensing problem. The 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 lets you include the zfs kernel module on any archiso without creating a custom one.

Archzfs

The Archzfs unofficial user repository allows one to install the ZFS kernel module in multiple ways.
We need compile current kernel zfs module using DKMS method, to let it match current booted kernel. 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

Wow, that's slow...

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