In a hybrid approach, is it feasible to have a 2-node SoftNAS deployment on-premises that tiers data out to (and back from) public cloud? Or do we need to replicate SoftNAS on-premises to SoftNAS in Azure/AWS?

We can put a pair of HA enabled nodes on premise for local storage and connect to Azure/AWS for cloud capacity. We do indeed enable replications and/or snap shots to the Azure/AWS hosted instances. Separate shares on Azure/AWS can be used for expanded capacity. We do not do auto-tiering at this time (stay tuned).