Hi @Ben Morris
I understand the requirement, I have the same needs for few use cases. Unfortunately, there's no ETA for this feature yet. This is something the community is aware of. Getting this done depends on priorities as well as the complexity of this feature.
Regarding migration, data queued in a node can be used again if the node is brought back again. If this is not possible, you can spin up a new node and configure it to use the existing repos from the old node (they are not specific to a NiFi node). IMO this migration process will depend on your infrastructure. If you are on baremetal node with RAID local storage, this will take time as you need to bring back a new physical node with the old disks (if node recovery is not possible). If you are on virtual infrastructure, the task will be easier since you can create new VM, install NiFi and make it use the existing repos. Here also, time and complexity will depend on your storage type (local or network).
Working on HA/fault tolerance with realtime is not an easy task. You have lot of things to consider around data duplication. I am thinking out loud here but If you can afford at-least-once strategy, you can may be design your flow to achieve it (using state backend). There's no easy standard solution though. This will depend you data source, your ability to deduplicate data and so on. This is something I am working currently.
