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 offers multiple ways to install the ZFS kernel module.
We need to compile zfs module using DKMS method, so it will work with the running kernel.
In order to build the module, DKMS needs the linux-headers package for the running kernel.

How does it work

It uses Arch Linux Archive to install the linux-headers package required for DKMS.

How to use

Boot on any archiso, and run

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