So KDL is like another JSON or Yaml. FSL-1.1-ALv2 is an, almost but not really, open source license that after a 2 years becomes available under a real open source license. It's to prevent free loading from companies or something. Sounds fine to me actually.
KDL is more than just JSON or YAML. It's node based. It's output in libraries is effectively an AST and its use cases are open ended.