Regarding "unix philosophy" and ZFS... it's actually very compliant with it, despite uninformed claims from early public release about "blatant layering violations".

It's just that majority of users never have reason to see more than tiny signs of the layers hidden behind (mostly) 2 command line tools, and for various reasons those layers are compiled into one one module.

But the clean layered design is how LustreZFS happened :)

https://zfs.rent/ is very interesting.

I also recall someone working years ago on a way to push snapshots to S3 or similar, but I never heard if that idea got off the ground (downside is of course the snapshots need to be recovered before they can be mounted, but the dollar cost would be rock bottom).

What would be more interesting is a backup application for Desktop Linux that assumes a ZFS root; all the problems that plague Desktop applications (that seem to keep them in eternal beta or wither away) disappear. It needs to switch on and push snapshots. It needs allow the remote file system to be mounted (to browse the snapshots for selective recovery). It needs a a disaster recovery process to recover an entire system from a remote snapshot.

rsync.net already provides zfs receive capability: https://www.rsync.net/products/zfsintro.html