You can do whatever you want that provides the right dictionary. If you want to generate JSON and then parse that into a Dictionary, go ahead. It’ll be a little more expensive, but hopefully not too much.
I’m leery of the idea of exposing JSON data directly in the API. For one thing, I would like to move away from using JSON as the internal storage type in the database; it’s expensive to parse and generate. There are a number of more efficient binary formats with the same semantics. But we should of course keep this as an implementation detail and not expose it, which implies not letting the client app see the raw data format, only parsed data.