From within Python, all objects are supported by default. If you can parse it, you can glom it. You can even register additional behaviors for specific types to keep your specs tight: http://glom.readthedocs.io/en/latest/api.html#setup-and-regi... (example: http://glom.readthedocs.io/en/latest/snippets.html#automatic...)

The CLI is in a pretty preliminary state, usable but not as robust as it will be in a few weeks. It only supports built-in parsers (JSON and Python literals) What formats are you thinking? YAML?