OpenZFS definitely has enough information to uniquely identify an object within a pool (dataset id/object id pair). Skimming the NFSv4 spec, it seems like it should be nbd to put all datasets into a single virtual namespace. But thats me imagining NFS as a first-class interface to ZFS, rather that a standalone server using POSIX interfaces. Its quite possible we don't expose enough info for a server to use.
I'd be happy to chat to an NFS server person if they'd like to work with me on plumvong useful info our org ZFS for a server to use!
💚