I noticed in boxgrinder-build-0.10.2/lib/boxgrinder-build/plugins/os/rpm-based/src/appliance.ks.erb that there's support for --fsoptions via an options: key in a .appl file. However, that key isn't defined in any of the schemas in boxgrinder-core-0.3.12/lib/boxgrinder-core/schemas/ (and so a boxgrind-build fails with that key), so I wasn't sure whether that warrants a bug report or if the .erb simply hints at a forthcoming feature?
The KS file is used under the covers to feed into one of the programs we use behind the scenes to build appliances, it isn't directly editable by the user. Our own appliance file format is completely different, and a separate thing entirely.
Hope that clears it up.