This looks like a very interesting project as far as akka persistence goes. It's a great concept - managing migrations via a generic AST, kudos! It seems like a natural fit for the new 2.4 concept of EventAdapters.

I maintain a journal/snapshot plugin on mongo, and one of the features many users asked for (and got) was storing bson payloads (DBObject for casbah and BSONDocument for reactivemongo) directly in the journal to be able to inspect entries.

In the context of stamina, it would be great to have the ability to retain the json AST all the way through to Mongo. This wouldn't be a minimum serialized size choice or maximum performance choice, but there's something to be said for easy inspection.

From what I can see, at a minimum this would change Persisted to store the AST as JsValue or something like it (json4s JValue, play-json JsValue, etc). To support akka 2.3, there would also need to be some support for translating Persisted itself into the same AST format. Of course, akka 2.4 and manifests simplify the last part.