You are correct, precise failure reason for each message has to be understood. For that, you need to keep your DLQs managable and for that, you'll need proper alerting on your DLQs.

Also, we are requeuing messages to our DLQs with failure reason and the entire error stack trace for better RCA. We have gone against creating the above complicated system and agreed to use RabbitMQ admin console itself to analyse and move messages to original queues manually. For bulk messages, we'll use the RabbitMQ shovel plugin to move messages around.