While this might not need a fix, maybe just a note for future users that try this i ran into the following when trying to install on my low spec HP Cloud laptop, also would probably not run into these issues on more powerful computers
1st. Had to tell archlinux install environment to boot with more of a ramdisk (256mb by default) using cow_spacesize=1G at the end of the kernel parameters, otherwise the script would run out of space when downloading packages.
2nd. for some reason it never mounted the drives after formatting, causing it to install to the booted ramdisk, i got pass this by manually mounting and then running the script without formatting. (also note i formated it again with ext4 instead of btrfs, so i also had to manually set a label of ROOT, and also remove the rootflag "subvol=@" in the syslinux arch.conf
3rd. during install when it was compiling i kept running into OutOfMemory and it would kill an instance of the cc1plus process, i got past this by killall cc1plus in another console, although im not sure if this might have caused other problems, although everything mostly appears fine.
(Laptop Specs - HP Cloud 14, Celeron N3060, 4gb Ram, 32GB SSD seen as mmcblk0)
Otherwise nice work!