Karel is right, you can implement custom ExecutionResolver and achieve what you have propose.
But generally I like your idea, and I would actually go even further and implement support for JSR-353, objects JsonArray and JsonObject.
But Maps could be supported as well. For example as an adapter for JsonObject objects.
Would you mind to file a feature request?
I would actually appreciate if you could draft an implementation (in a fork of arquillian/arquillian-graphene · GitHub ) and eventually send a pull request for discussion.
But it's not strictly required. ;-)