Squashfs is indeed not compiled into the Globalscale kernel:
glasgall@latte:~$ zgrep SQUASH /proc/config.gz
# CONFIG_SQUASHFS is not set
You can build a kernel (following the instructions on the wiki) with support for it compiled in or as a module, but you’ll have to give up wifi support until Globalscale gives us source for the Marvell 8W8897 driver so we can build it for custom kernels.