Selector of type Dictionary in blueprints

I was hoping to make a blueprint which asked users for a dictionary of data. This would be used to make a notify service call in the automation like this:

service: "notify.{{ notify_service }}"
  title: Title based on triggering event
  message: Message based on triggering event
  data: !input extra_integration_specific_data

Doesn’t seem like this is possible right now. I imagine this would also be useful for other integrations as well. For example if you wanted to provide an automation which turned on a light in a flexible way but didn’t want to create an input for every possible option in the light.turn_on service, could just ask for a dictionary instead.