Hm that's an interesting idea, thanks for sharing this! How exactly do you perform the restart of the Celery service and where are your queues configured? I guess you don't specify them in /etc/defaults/celeryd?
Correct, we didn't use /etc/defaults/celeryd, or use a standard init/systemd/upstart/etc-based way of starting celeryd. Instead we used daemontools to add and remove celeryd processes with their own configuration. It took a bit of work, but ultimately let us do code updates with zero downtime.