Scaling out a _service_ that uses data managed by ZFS is where NFS helps you. You simply mount the same ZFS storage in multiple hosts via NFS.
If you meant scaling ZFS itself such that the shared storage is resilient to a full host failure, I’m afraid ZFS is not your best bet. ZFS scales vertically very nicely. Heck, I have a single host with 2 X 100G NICs and 4 x 40G NICS fronting 1.2 PB of ZFS managed disks. If that host goes down, say from a motherboard failure, all 1.2 PB becomes inaccessible until I can hook up the JBODs to a different host physically.
If you meant scaling ZFS itself such that the shared storage is resilient to a full host failure, I’m afraid ZFS is not your best bet. ZFS scales vertically very nicely. Heck, I have a single host with 2 X 100G NICs and 4 x 40G NICS fronting 1.2 PB of ZFS managed disks. If that host goes down, say from a motherboard failure, all 1.2 PB becomes inaccessible until I can hook up the JBODs to a different host physically.