Is it possible to include this as an automated process rather that having to jump through loops trying to get the other Sqaushfs resize methods working? Not sure about other versions of Sqaushfs but the one on Banana Pi R64 does not do anything.
squashfs itself is read-only, it can't be resized (and it's always as large as it needs to be, after compressing; variable). The only things you can change, are a) the size allotted for the kernel and b) the default starting size of the writable overlay (which may use a number of different filesystems, some easier to resize than others, among them jffs, ext4, f2fs). For an 'easy' process, the filesystem in question needs to support online resizing (at least growing), but you probably will have to set up the firstboot environment accordingly.