David Smith in the mailing list has already begun work on this. The link to his current set of code in Github is here: https://github.com/helicopterman22/nifi_amqp_processors
He is seeking help with licensing/unit testing/etc.. so that it can end up in a build.
We have word from another user now that they too are interested in this. They specifically are using RabbitMQ but we should be able to implement (ideally) a pure AMQP protocol friendly version and be good to go.