Would be keen to know if this passes Jepsen style tests now

There are some limitations when using Quorum Queues, this was only patched recently - https://github.com/celery/celery/issues/9149

Does that do HA/replication/clustering etc though?

Sounds like PGM

Similar ideas, yes. But somehow I found Aeron and got it to work, not so straightforward with PGM. Been a while now, so not sure about the details.