> maintain my own kernel updates Not really: zfs is available in aur as a dkms package. Pacman automatically rebuilds dkms modules when it updates the kernel.

> maintain my own kernel updates Not really: zfs is available in aur as a dkms package. Pacman automatically rebuilds dkms modules when it updates the kernel. All you'd need to do is modify mkinitcpio.conf to include "zfs" in the HOOKS at the appropriate stage. So: more complicated that just using ext4, but not "maintain my own kernel" level of difficulty.