You can replicate via SnapMirror to another site where the DR side has a FabricPool. ONTAP supports multiple tenants for S3 providers too in 9.7. I'm not sure what the ask is here? Maybe I'm missing something. I'm not familiar with Ceph so that may be what I am missing.
StorageGrid is still your best bet here. It can run in a containerized environment or as VMs either of which can have FAS storage behind the covers. It is much much more robust than Ceph and the best part is you can mix VMs and appliances. That means later you could buy appliances to add to the grid and free up your FAS storage.