OPNsense 25.1 has been released. I'll update in a week or two, it looks neat.
My OPNsense instance is a VM running on a Proxmox host, where Proxmox uses ZFS as its storage. I doubt the ZFS support within OPNsense will be applicable, I think it sees a raw block device. I wouldn't want OPNsense to create a ZFS filesystem using the blocks which reside within the Proxmox ZFS filesystem. While I'm sure it would work, it seems like it would just be confusing without really being beneficial.