We don't do backup dedupe as Windows has a decent implementation of one (off-line and not eating much of memory and CPU cycles). We do have a in-line dedupe for VMs. Something Microsoft don't really have.
Think about StarWind as a complimentary rather then a competitive thing to Windows ecosystem.
Keeping in mind open source file systems are not supported by Hyper-V (and have very low chances being suppoted, think about why NFS is out of game for years) I would not count on them. But you're right, DFS
is a bad thing (IMHO) and what you mention with a second link could be a replacement for it (file-level replication). Together with a Hyper-V Replica (VM level replication) and StarWind replication (LUN level). All
parts of the puzzle