The task needs to be able to specify everything that needs to be in the policy file so that the butler can put and get data for a new dataset type.

Consider that the policy data can be split between the camera-specific and the task-specific parts. (KT was thinking of calling the camera part the "genre"), this potentially reduces the amount the task has to specify.
Another option is to hard-code some some of the policy in the butler itself:

• the path template (it could be assembled out of the data id components)
  • if it's hard coded the task must pass the component dataId keys
  • if it's not hard coded the task must provide a template
• python type
• storage type

there could be user overrides too.