This sounds like something you should pursue on the project’s GitHub page: https://github.com/immich-app/immich

The problem with managing replication outside of PVE is ‘what do you do when you have to move the VM/CT to another node?’ Are you going to move the conf file manually? It’s too much manual work.

Let PVE manage all of the replication. Use Sanoid for stuff that isn’t managed by Proxmox.

Home assistant integration could accomplish this for you. Not sure if it’s less work than regular mobile clients, though.

I think fans of Nix and NixOS would agree.